I often hear 50-year-olds saying, “I’m getting old” and see some of them practically hobbling along, as if in time to their own script. But then I know 70-year-olds who say, “I keep forgetting I’m not 16!”—like my mom, who bikes around a big city for miles, takes adult professional ballet classes for an hour and a half a day, and chainsaws trees down and repairs her rooftop on the weekend. Certainly, genetics plays a factor here: Some people are born lucky. We also know that living through stressful life experiences—things we can’t control—can accelerate aging: Some people are unlucky. But there’s an important caveat that has to do with how our luck—or lack of it—plays out over a lifetime. There is growing evidence that how some genes are expressed—for good or ill—has to do with how we choose to live. Meanwhile, how our bodies respond to stressful events turns out to have a lot to do with how we live—the things we can control. For example: If compassion and community service are an integral part of our life, the effects of the stressful life experience …