By Ned Potter

B O S T O N, May 29— Charlotte Chipman never exactly planned to see her 101st birthday. "I've just lived from day to day," she says with a shrug.

It is not an unhappy shrug. Chipman still lives independently in an apartment in the Boston suburbs. She goes to yoga classes. She spends a lot of time at the local community center. Neighbors are constantly dropping in.
Chipman is extraordinary — but she is becoming less so. Centenarians are the most quickly growing segment of the American population. In 1980 there were 15,000 of them; today their numbers have more than tripled.
What is their secret? Why do a select few live comfortably into a second century?

Researchers say, remarkably, that the centenarians they study tend to be far healthier, for far longer, than most other people. They manage to escape, or put off, the ravages of heart disease, stroke, lethal cancers, dementia and diabetes.
"They are on a very different trajectory than the rest of us," says Dr. Thomas T. Perls, director of the New England Centenarian Study at Boston University Medical Center.
"Instead of it being the case of 'the older you get the sicker you get,' it's much more the case of 'the older you get the healthier you've been."

Reuben Landau may be proof of that. Technically, he is not a centenarian yet; his 100th birthday is not until December. But at 99, he is still practicing estate law, poring over wills and stock tables with his glasses perched on his forehead. "I only wear them to keep dust out of my eyes," he says blandly.
Landau kept long hours at the office in his younger days. He smoked cigars. He salted his meat.
Then, at age 59, he had a heart attack. But unlike many other who go through such an experience, he's been fine since.
"It changed me," he says. "I avoided confrontations, I avoided tension, whereas before I tried to mediate."
Today he says he lives healthily. He exercises twice a day to move his joints. "I am more limber now than I was many years ago."

Researchers Say a Healthy Lifestyle Means a Longer Life
Perls watches such people for clues as to how the rest of us can live
better. He and other researchers theorize that most people are genetically equipped to live to their mid-80s.
Centenarians probably have something in their genes to allow them to live longer. Longevity does tend to run in families, including Landau's. But Perls says that's only part of the equation.
It helps to be wealthy, and to live in a place with clean air, but that's only part of the equation as well.
The largest factor, say doctors, is lifestyle — eating right, getting exercise, keeping one's weight down, avoiding smoking.
"We probably should do everything our mothers told us to do, except maybe clear our plates," he says with a smile.

And there's one other thing. Doctors say healthy centenarians tend to be assertive and purposeful. They are busy. They get out a lot. They attract friends. They do not spend decades in decline.
"Don't quit working, unless you've got an adequate substitute," says Landau. "You make a trip around the world, but then what? You read all the books you want to read, but what do you do after that?"
He grins at a younger visitor. "That goes for you too," he says.

Dr. Thomas Perls, who is seeking new volunteers for the New England Centenarian Project, has posted an interactive calculator online to allow people to estimate their life expectancy. You can find it at: http://www.livingto100.com.