He Said He Was the World Healthiest Man. Then Came a Stunning Diagnosis.

“Why do you want to live to 150?”

The question hung in the air. It was last fall, at a dinner during an invitation-only retreat in Aspen, Colo., filled with leaders in fields like foreign affairs, economics and entertainment.

Among them was a visionary of another sort — Bryan Johnson, the wealthy tech entrepreneur and so-called biohacker who has been waging a public and provocative fight against mortality.

He says he has poured millions of dollars into studying and perfecting his own body, and calls himself the most measured human being in history. His goal is to make it possible to live forever. (He is almost 49.)