David Sinclair's personal testosterone levels decreased until he improved his health and fitness, after which his biological age decreased from 58 to 31.

“And I could see for me, my testosterone levels were steadily, levels were going down. - And then you got tenure and they went back up again. [both chuckle] - No, I actually became complacent. And it was the worst. Actually my age changed in the wrong direction after that, 'cause I was relaxed. - Interesting. - And not worried about the future. But then I got serious. And I actually, according to the InsideTracker algorithm, got my age down from 58 to 31 in a matter of months.”