YOUNG LEE, 88, was not an athlete in her youth. She didn’t even learn the slow, graceful martial art of tai chi until 1999, when she decided to retire from her tech job because of a ruptured disc, Lyme disease and vertigo. Lee then signed up for a tai chi class at her local senior center in Edgewater, Maryland, and found that the practice helped restore her strength, stamina and overall health. So when, in 2004, the tai chi instructor invited her to take over one of his classes, she signed on. “Tai chi helped me recover,” she says. “I want to give that help to others.” —Thomas Ferraro