From the moment we are born, we begin to die. Aging is a universal but uniquely personal experience. It scares us, bullies us, and motivates us to live better. Because we, as a species, are living longer and longer (more than eighty years nowadays in most high-income countries), every one of us has even more time than ever before to grapple with aging and mortality. Despite what advertisements and doctors may tell us, there is no way to simply “turn back the clock,” but we still try to delay the inevitable. We all search for ways to prolong our lives and preserve our bodies—these complex...