WHY WE WILL LIVE LONGER . . .AND WHAT IT WILL MEAN The one-two punch of healthier habits and biomedical breakthroughs could push life expectancy past 90. Get ready for a brave new world.
By Richard I. Kirkland Jr. REPORTER ASSOCIATE Rosalind Klein Berlin

(FORTUNE Magazine) – Hope I die before I get old. PETE TOWNSHEND 1966

The generation that once rocked to that mocking line from the Who is within bifocal range of 50. And guess what? Baby-boomers have to find a new tune. The 76 million Americans born between 1946 and 1964 not only are the largest generation, but are set to become the longest-lived in U.S. history as well. No other change due in the 21st century will so profoundly alter the way we live. This upheaval-in-the-making didn't begin with the boomers, of course. The two age cohorts just ahead of them will push the old limits too. In 1900, average life expectancy from birth in the U.S. was a mere 47 years. By 1970 it had climbed to around 71. Since then, while most of us were looking elsewhere, it has gone up again, to 76. To be precise, that's 72.7 years for American men and 79.6 for women.

Even if this remarkable upward trajectory ended tomorrow, more than half of you reading these words could still expect to live past 81. That's because the longer you live, the better your odds. But it's not going to flatten out. Among experts on aging, even the most conservative agree we should be able to add three or four years to life expectancy over the next five decades. Others think we can do far better than that. Says Dr. Edward Schneider, 53, who heads the Andrus Gerontology Center at the University of Southern California: ''If we do things right over the next few decades, at least half the baby-boomers might expect to live into their late 80s and 90s.'' A few wild-eyed optimists even contend that by cracking the secrets of our genetic code we can live much, much longer. For all you restless baby-busters and aspiring fortysomethings with one eye on the corner office, here's a terrifying illustration of the sort of paradigm-shattering change they have in mind. Four words: 100-year-old CEOs! Who's right? In FORTUNE's view, the way to bet is on lives that will increasingly stretch out toward 90 and beyond in the years ahead -- with considerable potential on the upside. A host of consequences adhere to that extraordinary prospect. Many are already beginning to be felt, though the biggest shocks are a few decades away. Among them: Inheritances will get smaller, as long-lived elders consume capital that once flowed to the next generation. (Priced a nursing home for your folks lately? One upscale nursing home in Westchester County, New York, prefers to see that Mom or Dad has $500,000 in liquid assets before it considers taking one of them in.) Extended and multiple careers will become the norm, and the prevailing retirement age (now around 60) will creep back toward 70 as a growing number of older workers choose -- some from necessity, some for fulfillment -- to remain in the labor force. When Social Security was enacted in 1935 and the retirement age was set at 65, average life expectancy was around 61. The system won't stay afloat unless it is rebuilt into a means- tested welfare program for only the poorest of the elderly. Are we ready for this? Are you kidding? According to recent polls, most Americans do not expect to live into their 80s. So far, the age at which most of us retire continues to go down, not up. Most taxpayers are acutely aware that America's aging will impose a huge burden on Social Security -- after all, isn't that one of the main reasons payroll taxes have been rising steadily since the late 1970s? What they don't realize -- as the chart reveals -- is that if life expectancy reaches 80 in the next few decades and keeps on climbing, Social Security's bean counters will have woefully underestimated the future size of America's older population. Richard Suzman, the respected chief of demography at the National Institute on Aging (NIA), believes that by 2040 the number of Americans over 85 could top 30 million, up from 3.3 million today. For an upbeat glimpse of what could be in store, consider the long and still unfolding career of John Marks Templeton, 81: author (eight books), father (five children), grandfather (16 grandkids, so far), great-grandfather (two), and world-beating stock-picker. Sixteen months ago, after 53 years in the investment business, he finally retired, selling his wildly successful Templeton fund group and its $21 billion in assets under management to Franklin Resources of San Mateo, California, for $913 million. His share: $400 million. Now the Tennessee-born Templeton, who became a British citizen in 1963 after he moved permanently to Lyford Cay, Nassau, and collected a knighthood for his philanthropic work, jets around the globe supervising more than 30 charitable projects backed by the four foundations he has established. ''I'm working as hard as I ever did,'' he reports, with no plans to slow down. Last year Templeton edited and contributed to a collection of essays, by various experts, called Looking Forward: The Next Forty Years. ''It's such a joy to learn about the new things going on in the world,'' he says. ''This is the most exciting era in history. I wake up every morning fairly sizzling with enthusiasm.'' MOST OF US will enter our 80s with considerably less capital than Sir John -- and simmering, not sizzling. But since most of us will enter them, we'd better start thinking hard about how we aim to spend that extra time. Because the whole world is rapidly aging, this adjustment will ultimately pose a global challenge. When it comes to average life expectancy, the U.S. is outpaced by more than 15 countries, led by Japan, where at birth it's now 79 years. Still, two things put America in the vanguard of the longevity revolution: the unrivaled vigor and duration of its postwar birth explosion, which guarantees it an unrivaled cohort of octogenarians, nonagenarians, and centenarians four decades from now; and its role as planetary hotbed for the biomedical and genetic research that's likely to produce major breakthroughs in our ability to add years to life and -- most important -- quality to those extra years. What are the advances that will make us live longer and healthier? They range from the marvelous to the mundane.

-- More targeted medical weaponry. ''Many who used to get sent to heart transplant centers can now be put on medical management and handled outside a hospital without surgery,'' says Kenneth Manton, director of Duke University's Center for Demographic Studies. ''That's the difference biomedical research is delivering and will continue to deliver.'' No group will benefit from this difference more than older persons, since 80% of fatal heart attacks occur among those over 64 and 80% of cancers appear after age 50. Take hypertension. The diuretics of the 1950s lowered blood pressure and deaths from cardiovascular disease by draining the body of salt. This often had nasty side effects, such as raising the risk of diabetes. Each subsequent advance in treatment -- beta-blockers in the 1960s, calcium channel blockers in the 1970s, and so-called ACE inhibitors in the 1980s, which work by blocking the kidney's production of the hormone that causes blood vessels to - constrict -- has improved the treatment of hypertension with fewer side effects. Like those first diuretics, most cancer treatments are still the medical equivalent of using carpet bombing rather than smart bombs. But over the next two decades, rather than blast patients with massive overdoses of radiation or chemotherapy -- killing healthy cells as well as malignant ones -- doctors will learn how to fire computer-designed compounds directly into affected organs. That should translate into lower doses and longer, higher-quality life.

-- Better brains through chemistry. For most people, the greatest terror old age holds is the fear of losing one's mind. It's most cheering then to hear this prediction from Zaven Khachaturian, who directs the lion's share of the $200-million-a-year research program on Alzheimer's disease at the NIA: ''Within six years we should come up with treatments that will slow the brain's deterioration enough to enable Alzheimer's victims to function for another decade. In ten to 15 years, we might even be able to prevent this disease.'' According to the NIA, some four million Americans today are afflicted with Alzheimer's, a virulent form of dementia that riddles the brain with clumps of protein plaques and tangles and brings on a relentless slide into mental oblivion. This epidemic could explode as America ages. According to recent estimates, 6% of people ages 65 to 74 have the disorder, and nearly half of those over 85 show signs of it. More than 100,000 Americans die of Alzheimer's each year, putting it right up there with the nation's major killers: heart disease (800,000 annual deaths), cancer (200,000), and strokes (150,000). Lucky sufferers expire within five years; the unfortunate stay alive up to two decades. ''If curing heart disease and cancer means we get to stick around and die of Alzheimer's,'' says medical researcher Roderick Bronson of Tufts University, ''we'll look back on them as our friends.'' The war against Alzheimer's is progressing on two fronts. Warner-Lambert has just begun marketing Cognex, a limited treatment that works in a handful of cases and then succeeds only in allowing the patient to function for an extra six to nine months. But several major drugmakers, notably Bayer, are testing in animals a more effective second-generation treatment that works by blocking the accumulation in neurons of toxic levels of calcium -- one of the ways those tangles are formed. Researchers in Sweden are even testing on humans what may become the third-generation treatment, compounds that stimulate nerve-cell growth. Geneticists in the mid-1980s pinpointed the location of the genes connected to an inherited form of Alzheimer's, which tends to strike much earlier, in the 40s and 50s. And last fall a team led by Dr. Allen Roses of Duke University Medical Center announced it had identified a gene -- called ApoE 4 and ensconced on human chromosome 19 -- that is strongly linked with the onset of late-stage Alzheimer's. Doctors will use such genetic markers to identify people most at risk and start them on preventive treatments as these become available. Eventually, healthy nerve cells may be injected directly into the brain, where they will grow, make the right connections, and replace dead neurons. ''That's pretty futuristic stuff,'' says Khachaturian. ''But it's definitely coming down the pike, perhaps in 20 years.'' Such treatments, along with new memory-enhancing drugs, would also benefit stroke victims and those suffering from spinal injuries or Parkinson's disease and other neurologic disorders. In the not-too-distant future, people may chew pills to fend off dementia the way middle-aged men now munch baby aspirin to prevent heart attacks.

-- Beefed-up bug fighters. Body parts don't age at the same rate. But one universal characteristic of getting older -- and the reason we become increasingly vulnerable to everything from cold viruses to cancer -- is a steady falloff, starting around age 30, in the effectiveness of our immune systems. Part of the problem seems to reside in a class of lymphocytes, known as T-cells, that attack infected cells directly and also serve as messengers to mobilize the rest of the immune system. As we age, the number of T-cells produced by the thymus gland declines, while the percentage of them already in the bloodstream but no longer functioning rises. Getting rid of these so- called effete T-cells, one theory holds, should encourage the thymus to get cracking and put the immune system back in fighting trim. Gerontologist Edward Schneider believes a drug to do that will be developed in five years -- and he's hoping to get there first. Schneider and some colleagues launched a biotech startup, Rejuvon, last year and are currently chasing venture capital.

-- Hormone cocktails. Remember hormones? These are the body's chemical messengers that turn genes on or off and regulate how tissues and organs grow and repair themselves. They're also what, in our early teens, made our shoe sizes surge from eight to 11, our pores gush oil, and even not-so-close encounters with the opposite sex a dizzying experience. As the years accumulate, many of us stop pumping out enough of this bodacious stuff. Levels of human growth hormone, which helps keep us lean as well as make us taller, decline with age in about half of all adults. Researchers have also learned that, just as women during menopause experience a sharp drop in production of the female sex hormone estrogen, most men aged 60 and older manufacture markedly lower amounts of the male sex hormone testosterone. The linkage between hormone levels and health, though still poorly understood, is formidable. Estrogen replacement therapy dramatically slows the bone thinning that develops into osteoporosis and cripples millions of older women. It also significantly reduces in most females the risk of heart attack and stroke. In men, testosterone injections can strengthen muscles and counter anemia, while a related hormone, known as DHEA, has been shown in animal tests to revive aging immune systems and even deter cancer. In the most dramatic display yet of hormonal firepower, Daniel Rudman of the Medical College of Wisconsin in 1990 injected human growth hormone into elderly men whose levels of it were unusually low. Within months their fat shrank by 14%, their lean body mass expanded by 9%, and their skin increased in thickness by 7%. The overall effect on physique, he reported, was equal to shedding ten to 20 years. These remarkable results have since been confirmed by other researchers. They have also spawned a cottage industry of Mexican longevity clinics that supply American and European clients with doses of the high-priced drug, which costs $13,000 for a year's supply. The real problem with hormone treatments, however, isn't their expense; it's their potentially devastating side effects. Use of growth hormone over long periods -- and to be effective it must be taken continually, or else the magical results vanish in a Dorian Gray-style reversal -- often results in carpal tunnel syndrome, other kinds of joint inflammation, and diabetes-like symptoms. Estrogen and testosterone may increase the risk of cancer in some recipients. Still, as more research leads to a better understanding of what dosages are proper -- and how best to deliver them -- such therapies could become more widespread. Within five years Rudman believes that physicians may be allowed to use growth hormone for short-term therapies -- to accelerate healing of wounds, say, or to enhance the ability of some underweight elderly to absorb nutrients. Further down the road, he says, older patients in 20 years may well visit doctors to have their hormone levels checked and get prescriptions for ''custom-tailored cocktails'' that will help them stay fit.

-- New, improved, fat- and smoke-free lifestyles. ''No drug in current or prospective use holds as much promise for sustained health as a lifetime program of physical exercise,'' says Dr. Walter Bortz of Stanford University Medical School, a 20-miles-a-week jogger at age 63. That view, backed by a growing body of evidence, can no longer be dismissed as the raving of fanatics on perpetual endorphin overdoses. ''Exercise is one of the real breakthrough areas in the research,'' agrees Dr. John Rowe, 49, president of Manhattan's Mount Sinai Medical School and Hospital, who was a 1988 recipient of a MacArthur Foundation grant to develop ways to encourage successful aging. Studies have shown, for example, that in addition to its familiar cardiovascular benefits, working out stimulates the body's production of growth hormone and improves the functioning of the immune system, especially among older people. Says Bortz: ''Exercise for young people is an option, but for older people it is an imperative.'' In addition to lacing on those jogging shoes, don't neglect to eat your spinach -- and your carrots, kale, broccoli, oranges, and bananas as well, all of which are high in vitamins E and C, as well as beta-carotene. Why? It has long been known that as the human body merrily goes about its basic business of converting glucose and oxygen to energy, it spews out a torrent of so- called free-radical molecules. These cause damage to proteins, membranes, and ultimately the DNA in cell mitochondria -- the place where the energy we run on is generated. Free radicals have been implicated in many of the changes that accompany aging and appear to play a role in cancer, arteriosclerosis, cataracts, and nerve damage. To defend against such wanton self-destruction, however, the body also produces antioxidants that react with and disarm free radicals. Some are enzymes. The other natural antioxidants are, yes, good old vitamins C and E, and beta-carotene. (For more on what you can do to live long and well, see box below.) + A final arresting fact for anyone still skeptical about the efficacy of this get-a-lifestyle mumbo jumbo: Since the mid-1960s, the death rate from heart disease in the U.S. has plummeted by 50%. And do we owe this boon to the huge increase over that time in the balloon angioplasties and triple bypasses performed by gifted, dedicated, and highly compensated surgeons? No. Instead, almost every medical and epidemiological expert credits three sweeping changes. First and most important is the sharp decline in smoking -- the single most effective, legal way to shorten your life, and now practiced by only 25% of the adult population, vs. 40% in 1965. Second is the rise in exercise, especially among men. Third are dietary changes that have lowered the typical American's cholesterol count.

-- Putting on new pairs of genes. ''I'm not interested in adding three or four years to life expectancy,'' says evolutionary biologist Michael Rose, 38, a professor at the University of California's Irvine campus. ''I'm interested in 200-year-old humans.'' Say what? Since our ancestors got up off their four feet a couple of million years ago, the longest any human has ever lived, depending on which old coot or cootess you believe, is between 115 and 120 years. That barrier is our species' maximum life span. Breaking it, as Rose contemplates, will require more than simply fighting the manifold disorders of aging one disease at a time, as we now do. It will take nothing less than what gerontologists call ''a magic bullet,'' a fundamental assault at the molecular level on the upward sweep of mortality itself. If such a bullet is ever made, genetic engineering will supply the ordnance. Consider the lowly roundworm. By manipulating the genes of a species of nematode, Thomas Johnson of the University of Colorado has already doubled its puny 30-day life span. Michael Rose's lab has successfully doubled the maximum and mean life spans of a species of fruit fly. A series of fairly mundane experiments that seemingly do not involve genetics are helping scientists in their quest. So far, only one technique has consistently extended the life span of short-lived mammals, such as mice -- and it requires practically starving them. Caloric restriction, as it's known, adds health as well as years. In the most important such experiment yet, the NIA in 1987 began testing it on primates, our closest relatives in the animal kingdom. Because these animals have a maximum life span of 40 years, vs. 2 1/2 years for mice, the final results won't be in until many baby-boomers are wearing dentures. But already the animals on diets are reaching puberty a year or two later than their brethren who chow down as much as they please. The goal isn't to persuade us all to go on truly draconian diets (though let's face it, it does seem one more reason to shed a few pounds). Explains Richard Sprott, head of the NIA's biology of aging program: ''If we could understand how caloric restriction produces its effects, then we'd understand a great deal more about the basic biological mechanism of aging. And that would give us a way to intervene. It could provide that magic bullet we talk about.'' Michael Rose draws a parallel with the success of the U.S. space program after World War II: ''Sending men to the moon and back by the end of the 1960s seemed impossible too, until we decided to commit enough resources. Then the science developed. I know we can extend life span for a far smaller sum than the Apollo project cost. I'm doing it on a toy-model scale now.'' Consultant Kenneth Dychtwald, 43, whose firm Age Wave, in Emeryville, California, advises corporations like Johnson & Johnson, Kmart, and General Motors on what the graying of America means to their markets, believes such an investment is inevitable. Says he: ''Breakthroughs that humans have dreamed about for thousands of years are right around the corner.'' Exuberant prophecies like those, however, are still a minority. Most scientists, including the NIA's Sprott, suspect there may be hundreds of genes, rather than a handful, that interact to affect human longevity. That complexity, they argue, makes reaching into the genome and resetting the cellular clock a pretty remote possibility.

What we will see fairly soon is genetic repair of flaws that give rise to specific diseases. In the past year researchers -- aided by the monumental Human Genome Project, which aims to map our genetic code by early next century -- have identified a number of troublesome genes. Among the maladies they cause are Huntington's disease, amyotrophic lateral sclerosis (Lou Gehrig's disease), a form of colon cancer, and severe combined immunodeficiency, or SCID (a rare condition, better known as ''the bubble boy disease,'' in which the immune system virtually ceases to function). By injecting several children suffering from SCID with a healthy copy of the defective gene that causes it, doctors have succeeded, for now, in revitalizing the immune system. More than 40 other trials are being conducted to test this sort of gene therapy's efficacy on cystic fibrosis, cancer, and AIDS. EVEN WITH ALL THIS, lifting average life expectancy toward 90 and beyond will require solving some daunting arithmetic. Here's the problem: Because we've already conquered most of the infectious diseases that once killed large numbers of children and young adults, the gains we're making now come from adding a few extra years to an already long-in-the-tooth crowd's lives -- and not six or seven decades to the lives of kids. As a result, future victories over disease -- even major triumphs -- will inevitably deliver small gains in life expectancy compared with those won earlier in this century. Demographer Jay Olshansky of the University of Chicago Medical School calculates that completely wiping out cancer in the U.S. would add only 3.2 years to average life expectancy from birth. Eliminating heart disease would lift it by just three years for women and 3.6 years for men. ''There's a large element of wish fulfillment in these optimistic projections about extending life expectancy,'' argues Dr. James Fries of Stanford University, who along with Olshansky is a leading proponent of the view that there's a ceiling on average life expectancy of around 85. Indeed, the way Duke's Ken Manton gets life expectancy to 100 is by assuming that the entire U.S. population adopts and maintains optimum health habits throughout their lives. Wanna bet? On the other hand, neither camp takes into account the enormous wild card of genetic engineering because its potential is impossible to model. And yet, most experts agree breakthroughs will happen -- and have a sizable effect on longevity. Says the NIA's Dick Sprott: ''Over the next 25 to 30 years, we're going to produce a tremendous change in the number of humans who will make it to something close to the species maximum.'' The social and economic consequences of this acceleration in life span will be far greater than anything now contemplated by most American policymakers and institutions. Take inheritance. A few years ago, economists Lawrence Kotlikoff and Lawrence Summers calculated that 80% of the country's capital stock has been piled up through intergenerational bequests. What happens to capital formation if tomorrow's long-lived woopies (well-off older people) consume that seed corn and leave almost nothing behind? Consider Social Security. As life expectancy rises toward 90, many Americans will spend almost as many years drawing a check from the government as they did working. This cannot stand -- not when, even on a conservative demographic forecast, the number of workers per retiree shrinks from 3.3 to fewer than two after 2010. How will Social Security survive then except as a pared-down, straightforward welfare program for the poorest of the very old? But how and when will we transform it? A society with more than 20% of its citizens over 65 will have to reengineer its physical as well as its fiscal landscape. Example: America's roadways -- their signage, the distance to off ramps, and the like -- seem optimally designed for 25-year-old males with excellent vision, quick reflexes, and high testosterone levels. But they can be deathtraps for the elderly. Since the mid-1970s, as the number of drivers over 70 rose sharply, deaths from car crashes among this group jumped 30% even though total fatalities among all drivers fell by 12%. Finally, a paradox. The longer we live, the more urgent it will become to learn how to die. In Greek myth, Tithonus is the pitiful soul who won from the gods the gift of eternal life but, lacking eternal youth, was condemned to live -- shrinking, shriveling, and longing for oblivion. Our nursing homes and hospital wards are filled with Tithonuses. There are many more who fear his fate. That grim fact is confirmed by brisk sales of books like Final Exit, the growing popularity of living wills, the record number of suicides among 65- and-olders, as well as the awkward career of Jack Kevorkian. Can't we as a society in the years ahead finally agree on better ways to decide -- among families and physicians and not by government diktat -- when it's worth fighting and when it's time to go? Hard questions, easier to pose than to answer. One obvious answer, though, is to at least stop doing things that make matters worse. Right now, the Social Security system appears to treat the fraction of over-65s who still draw a paycheck the way America's welfare system treats low-income working mothers. It encourages dependency. If you're 65 to 69 and earn more than $11,160 a year, your monthly benefits get cut by one-third. Since interest and dividends don't count as earned income for this calculation, this disincentive is aimed not at the well-off but at those who could most benefit from a little extra money. THE CULTURE still too often patronizes and stigmatizes its elderly citizens -- a phenomenon for which Dr. Robert Butler, 67, the NIA's founding director, coined the word ageism back in the late 1960s. Many corporations continue to push older employees out the door as fast as you can say ''early-retirement package.'' Few yet follow the example of Travelers Insurance, which created a job bank of temporary employees from a pool of retirees and younger workers and found their higher productivity saved it $1.5 million a year, or the Days Inn hotel chain, which began a concerted drive to hire people over 55 as reservation agents when it found that, compared with younger employees, they cost 64% less to train and recruit. The thumb rule offered by economist Larry Kotlikoff is that to keep the economy from slowing down, we should offset every 10% increase in life span with a 10% increase in the retirement age. Here's John Templeton's advice: ''Don't retire until 75.'' By all means, though, don't feel compelled to slog away at the same old grind unless you really love it. One large advantage of longer lives should be that they expand our opportunities for change. Such change may not involve highly paid work, unless you're self-employed. For some years yet, it will be difficult to find decent corporate jobs after age 65. But volunteerism can be personally rewarding and produce huge benefits for society. ''The key is to have a real purpose to your life,'' says Bob Butler, now chairman of geriatrics at Mount Sinai Medical School. ''Numerous studies confirm that when people have goals and a structure to their lives, they actually live longer and also enjoy better health.'' If you're not working or volunteering, take a course. Take a trip. Take a chance. Old men ought to be explorers, as the poet T.S. Eliot once observed. Old women too. Perhaps the most critical question raised by the longevity revolution is how healthy tomorrow's outsize elderly population will be. About seven million Americans today require long-term care because they are too mentally or physically frail to fend for themselves. The annual cost is more than $54 billion. But that figure doesn't begin to reflect the cost of treating the disabling infirmities and diseases of old age. According to the most recent estimates, Americans over 65, though just 12% of the population, account for 36% of personal health care spending. Unless we can shrink both the level of , disability among older Americans and the time they spend in poor health during their final years -- compress morbidity, in the jargon of gerontology -- we may eventually have to choose between bankruptcy and health care rationing on a distressingly large scale. IS THIS compression occurring? Various surveys confirm what our eyes tell us daily: The average 70-year-old today is considerably healthier than his or her counterpart 50 or even 20 years ago. In an important study last fall, Duke's Manton found that the rate of chronic disability among Americans over 65 may have declined by 5% between 1982 and 1989. But none of the evidence is conclusive. Says Laurence Branch, director of long-term-care research at Abt Associates, a Cambridge, Massachusetts, consulting firm: ''We're increasing life expectancy, but it's still not clear if we're increasing most people's active life expectancy -- the percentage of their lifetime they can expect to enjoy good health and independence. What is clear, however, is that we know we can do it.'' That upbeat attitude is worth keeping in mind, since in some ways the biggest hurdle an aging America faces may be psychological. The U.S. has never stopped thinking of itself as a young country, a frontier country -- a new world, not an old one. For such a people, growing up is hard to do. It's worth remembering, then, that alongside its many discomforts, long life has always been thought to bring with it large rewards -- among them, perspective, maturity, insight. William Butler Yeats said it best in his poem ''The Coming of Wisdom With Time'':

Though the leaves are many, the root is one: Through all the lying days of my youth, I swayed my leaves and flowers in the sun: Now I may wither into truth.

Maybe we will too.

CHART: NOT AVAILABLE CREDIT: FORTUNE CHART/SOURCE: CENSUS BUREAU CAPTION: A GROWING CROWD OF SENIORS How many oldsters? Social Security projections are the most conservative. Epidemiologist Jack Guralnik at the National Institute on Aging assumes recent big gains in life expectancy will continue. Kenneth Manton, a demographer at Duke University, thinks they may well accelerate.