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The New England Centenarian Study at Boston Medical Center began studying very old people and their offspring in 1995, setting out to determine — among other things — which characteristics people 100 and older seem to share. They differ in education, socioeconomic status, religion, ethnicity and dietary habits, but they have many things in common:

• Few centenarians are obese. In fact, men of 100 and older are almost always lean.

• They rarely, if ever, smoked.

• They seem to be able to handle stress better than most people.

• About 15 percent experience no significant changes in their thinking abilities as they age, disproving a popular notion that by age 100 everyone becomes demented.

• Many centenarian women successfully bore children after age 35, even 40. The researchers found that women who had children after 40 were four times as likely to live to 100 as were women who did not. But it is not the bearing of a child at an advanced age that conveys a very long life; rather, the ability to bear a child at that age indicates that the woman’s reproductive system is aging slowly, along with the rest of her body.

Beyond the centenarians themselves, at least 50 percent of centenarians have siblings, first-degree relatives and/or grandparents who were centenarians. Male siblings of centenarians are 17 times as likely to reach 100 as are other men born at the same time. Among women, the difference is 8 1/2 times.

Many of the children of centenarians (age range of 65 to 82 years) appear to be following in their parents’ footsteps, with marked delays in the onset of cardiovascular disease, diabetes and overall mortality. Also, in standardized personality testing, these offspring scored low on the neurotic scale and high on the extrovert scale, compared with published norms.

Will you live to be 100? No one can say, but the “Living to 100 Life Expectancy Calculator” was created by Thomas Perls, director of the New England Centenarian Study and a professor of medicine at Boston University. It involves 40 health, family history and lifestyle questions. To see how you stack up, go to livingto100.com.