HOW TO LIVE TO BE 120

To grasp what it means to be 120 years old, consider this: a woman in the U.S. now has a life expectancy of 79 years. Jeanne Calment of Arles, France, reached that advanced age back in 1954, when Eisenhower was in the White House and Stalin had just passed from the scene. Twenty-two years later, at age 100, Calment was still riding her bicycle around town, having outlived both her only child and grandchild. And 20 years after that, she was charming the photographers and reporters who arrived in droves last week, along with the French Minister of Health, to mark her 120th birthday.

The woman certified by the Guinness Book of World Records as the oldest living human allowed that she was “very moved” by the celebration. How does she feel? Like half the people over 85, she no longer hears very well. A broken hip five years ago left her unable to walk, and cataracts have robbed her of vision. (She has refused surgery, says her physician, Victor Lebre, because “she thinks it’s normal at 120 not to see.”) But there is no question that her wit is intact. Asked what kind of future she expects, Calment didn’t miss a beat: “A very short one.” As for her Methuselan achievement, “It’s not impressive at all,” she insisted. “It’s natural to grow old.”

True, of course, but 120 borders on the unnatural. It is at the uppermost limit of what biologists believe is the maximum human life-span. Calment, says Harvard geriatrician Dr. Thomas Perls, “is the Michael Jordan of aging,” genetically blessed with extraordinary physical gifts that favor survival. “The chances of you or me getting to be her age are similar to our chances of playing basketball like Jordan.” Only one other person is known to have lived as long: Shigechiyo Izumi of Japan, who died in 1986 at 120 years.

Whereas few of us can expect to be longevity superstars, demographic trends show that more and more of us will at least make it into the big league. The “oldest old”-those 85 and older-make up the fastest-growing segment of the population in the U.S. and other prosperous nations. Between 1960 and 1990, while the overall U.S. population grew 39%, the ranks of those 85 and older jumped 232%. The U.S. Census Bureau projects that by the year 2040, there will be 1.3 million Americans 100 years or older; some demographers put the figure at 4 million.

The picture of 4 million doddering, medically needy centenarians is not pretty, but the prospect may not be so grim. People who make it past 85 are a hardy group, says Richard Suzman of the National Institute on Aging. About 30% still live in the community and “are robust in the sense that they are able to lift shopping bags, walk half a mile and climb stairs.”

The oldest old are healthier than the merely old in several respects. Heart disease and stroke, for instance, have their greatest im-pact in the 50s through 80s for men and about 10 years later for women. Those who make it past the danger zones are less apt to be stricken at all. Similarly, Alzheimer’s disease usually picks off its victims by the mid-80s. Perls found that men in their 90s outperformed octogenarians in tests of mental function.

The Grim Reaper himself may slow his pace for the oldest old. While the chance of dying increases exponentially with each year from 50 to 90, the odds rise less steeply after 90.

The vigor of the very old has a simple explanation, says Perls: “The genetically weak die off, and what is left is an enriched group of healthy, strong individuals.” This weeding-out process is most evident among those for whom the selection pressures are greatest. For instance, while death rates are higher for African Americans than for whites up to age 75, blacks who make it to 75 have superior health and longevity. Similarly, although men have a shorter average life-span than women, males who do survive into extreme old age tend to be in better shape than women. Men make up 20% of 100-year-olds and 40% of 105-year-olds.

If there’s a secret to long life, it is surely in the genes. Calment’s mother lived to 86, her father to 93. Scientists speculate that long-lived people may carry genes that confer special resistance to the assault of free radicals, chemical residues of metabolism that do increasing damage to DNA as the years roll by. Researchers are also looking at apolipoprotein E, a substance that ferries cholesterol to and from cells. People vulnerable to Alzheimer’s and heart disease tend to have a certain type of gene for this protein, while those who live longest tend to have another type.

Temperament, also genetically mediated, may play a role in longevity too. Perls, who is studying 100 Boston-area centenarians, notes that whereas they all have seen their children, siblings and friends die, they “handle stress incredibly well.” A life-style of moderation and exercise also helps, as does education. Studies suggest that, on average, better-educated people suffer less mental deterioration in old age.

As for Jeanne Calment, she seems to embody the calm resilience associated with long life. “I took pleasure when I could,” she said last week. “I acted clearly and morally and without regret. I’m very lucky.”

-Reported by Alice Park/New York