That’s a pretty large if—the idea of living for a century and a half is not inconceivable, though it is far-fetched at the moment. But what interests me about someone like Hanley, a mathematical biologist who splits his time between California and Idaho, is that, unlike most people, he lives as if it’s a real possibility.

Hanley’s path to super-longevity is still hypothetical. He develops gene therapies through Butterfly Sciences, a small company he founded, and has been testing a therapy on himself that he believes might extend his life span and, crucially, his “healthspan,” the period when he’s in good physical and mental shape. He hopes that future advances—among other difficulties, current gene therapies can’t modify a sufficiently large share of cells in someone’s body—could extend those two spans even further.

The gene therapy Hanley has tried is not proven to lengthen lives; he says he hasn’t experimented with it on anyone besides himself, and he does not have FDA approval for testing the therapy. Matt Kaeberlein, the director of the University of Washington’s Healthy Aging and Longevity Research Institute, told me that gene therapies may someday become a common tool for dramatically extending human lives, but that this is unlikely to happen anytime soon. It’s “theoretically possible,” Kaeberlein said, but “for now, it’s pure science fiction.”