Living to 100 may well represent the ultimate game of "Survivor." Centenarians, as they're known, were alive at the turn of the last century, when airplanes, computers, and space travel were pure science fantasies. And yet, a century later, these centenarians are blazing new trails in science every day.

An estimated 70,000 Americans have reached the century mark. These "oldest old" now represent the fastest-growing segment of our population, growing by 35 percent between 1990 and 2000.

For Dr. Thomas Perls, centenarians are a source of endless fascination. Perls, a geriatrician at Boston Medical Center, is director of the New England Centenarian Study. "Profiling centenarians helps dispel these myths, the idea that, 'The older you get, the sicker you get.'"

In fact, the reality is, for those in their 100s, "The older you get, the healthier you've been." Perls explains, "They are healthy, but you have to realize that the reason they got there was because they had to live the vast majority of their lives in very good health. They either markedly delay or avoid the diseases of aging."

Perls' work began in 1994 as a study of centenarians living near Boston. Since then, Dr. Perls and his staff have expanded the study, examining all facets of these exceptional individuals who have outlived so many of their peers.

So what has he learned from these marathon men and women? For starters, there is no one formula for a long life. Centenarians are all over the map - exercisers and couch potatoes, educational levels ranging from grade school to grad school, diets ranging from vegetarian to meat and potatoes. "It's really an interesting spectrum of individuals," he says.

But there are common threads: Obesity is rare, as is a history of smoking. They manage stress well, tending not to dwell on their misfortunes. In fact, most show a streak of humor that endears them to friends and relatives, and helps cultivate a support network that may well boost their longevity. More than half have close relatives - siblings, parents, cousins or grandparents - who also reached advanced ages.

Perls divides centenarians into three categories: First, the "survivors," who've managed to conquor chronic diseases such as cancer, heart disease, or diabetes. Then there are the "delayers," who avoided these diseases until after age 85. Finally, and most intriguing, are the "escapers," who've reached age 100 with no signs of illness.

Women far outnumber men in centenarian circles, by a ratio of 85 percent to 15 percent. In general, women are physiologically stronger, able to survive chronic diseases, while men are more likely to die of heart attacks or cancer at younger ages. But the men who do make it hold some surprises. "The men turned out to be functionally better off than the women," Perls says. "I think it's because for a guy to reach that age, he has to be in spectacularly good health."

Perhaps his most surprising finding is how large a role genes play in aging. "In the past, aging was thought of as an incredibly complex situation involving thousands of genetic and environmental effects, all interacting with each other in such a way that it would be an incredibly difficult puzzle to understand," Perls explains. "But I think it becomes a relatively simple puzzle when, instead of looking at aging, one looks at exceptional age. It's clear that genes are playing an important role, and that's probably the most exciting thing to me."

Centagenetix, a biotech research company founded by Perls and his colleagues, has embarked on an ambitious project to examine centenarian DNA samples, in hopes of developing a profile of the "typical" centenarian genetic variations. They plan to use this template to identify which specific genes or genetic variations cause age-related illnesses.

Ultimately, researchers hope to uncover the specific biochemical pathways that these genes control, and then develop drugs that replicate them. "If you discover a longevity-enabling gene, you want to find out what it does," Perls says. "It's a window -- a way of understanding how these people age more slowly, and hopefully develop a drug that does the same thing as the gene, for those who don't have that gene or genetic variation."

But for now, Perls advises a positive approach: "Aging is an opportunity. It's not some horrible thing to be avoided, like the anti-aging industry would have you believe." He dismisses those who frantically search for questionable miracle products to "reverse" aging. Regular exercise, quitting smoking, and improving your diet would have far more impact on longevity, he says.

"It's much better to approach it in a realistic way, asking, 'What can I do to slow down the aging process a bit, and try to delay some the diseases of aging with good health habits.'" He advises, "Instead of fighting your genes, take advantage of them."