David Sinclair keeps a relatively strict daily schedule to stay healthy, which includes green matcha tea, polyphenols in a couple of spoonfuls of yogurt in the morning, and an occasional bite of 80% dark chocolate.

But Sinclair, a 54-year-old professor in the Department of Genetics and co-director of the Paul F. Glenn Center for Biology of Aging Research at Harvard Medical School, isn’t rigid about everything.

He doesn’t exercise every day nor sleep more than six hours a night usually, he tells GQ in a recent interview (standard guidelines recommend between seven to nine hours of sleep each night and 150 minutes of moderate-intensity exercise per week).

Still, he says his regimen has helped him stay biologically 10 years younger than his age—underscoring a modern phenomenon called reverse aging by combating age-related disease and decline.

“I think a lot of us think that when you’re in your twenties, you’re impervious to aging and illness, and what we now know is that the epigenetic clock starts ticking from birth and that what we do in our twenties does affect our ultimate longevity,” Sinclair tells GQ.

While research on delaying and reversing aging is relatively new, experts say it concerns your epigenetics. Longevity experts have outlined the 12 hallmarks of aging, including epigenetic alterations, cellular senescence, and chronic inflammation. Lifestyle factors and other interventions targeting one or more of these hallmarks may delay the aging process.

“Biological age is a much better representation of health status than birthday candles,” Sinclair previously told Fortune. “Birthday candles don’t tell you how well you’ve been living and they certainly don’t tell you how many years you’ve got left.”

He believes that we’ll one day be able to turn ourselves back 20 years. “I don’t see any reason why that won’t be possible,” he continued. “It’s just a question of when.”

So what is Sinclair’s secret to aging well and staying young? He began working on it in his early thirties. Here are the three ways the longevity researcher got started: