Based on current death rates, Jay Olshansky, a biodemographer at the University of Illinois, says that 3 percent of girls today will reach 100, and about 1.5 percent of boys. However, some longevity experts predict that these numbers will go even higher. James Vaupel, of the Max Planck Institute for Demographic Research, in Rostock, Germany, believes that "a majority of children born since the year 2000 will celebrate their hundredth birthdays" and that "life span increases can continue indefinitely."

Through a variety of studies, longevity experts are identifying key factors that contribute to long life spans, including genetics, lifestyle choices and exercise habits. Researchers estimate that 25 percent of life span variances can be attributed to good genes, and the remaining 75 percent to environmental factors, such as exercise and diet. But, says Nir Barzilai, director of the Institute for Aging Research at the Albert Einstein College of Medicine, in cases of extreme longevity, genetics probably play a greater role. "For most of us, it is 80 percent environment and 20 percent genetics, but for centenarians it is probably 80 percent genes and 20 percent environment." By studying the elderly, he has found that a protein is present in higher than normal levels in the centenarians, which may protect them against Alzheimer's disease and diabetes.

Living right also contributes significantly to longevity, finds researchers. A Loma Linda University study found that Seventh-Day Adventists who maintain healthy habits live 10 years longer than those who did not follow a vegetarian diet and did not exercise regularly. A University of Cambridge study that followed 20,000 middle-aged men and women in England for 11 years found that participants with healthy eating and exercise habits could expect to live 14 years longer than people with poor lifestyle habits. Researchers are also studying the diet habits of centenarians living in Okinawa, where there are five times more people over the age of 100 than in the United States.

Not surprisingly, studies looking at exercise as a contributing factor have also found that regular exercise is one of the "strongest predictors of a long life." A 2006 study of 5,000 people living in Denmark determined that people who exercise regularly generally live five to seven years longer than people who are inactive. "Exercise is roughly equivalent to an oil lube and a filter for a car. You don't have to do it, but when you do it makes the car run a lot better," says Olshansky. Moreover, Thomas Perls, a geriatrician at Boston University Medical Center, who is studying 1,200 present and past centenarians in New England, has found that participants are able to avoid disability well into their 90s. "With healthy behaviors, you are adding years to your life, and you compress the time with which you experience disability," he says.

News Release: How to live to 100 www.forbes.com  April 7, 2009