Tech CEO Bryan Johnson is spending millions to be 18 again, but a longevity expert says his ‘heroic discipline’ is unsustainable

Forty-five-year-old Bryan Johnson’s $2-million-a-year attempt to reverse aging has left longevity experts both fascinated and highly skeptical—largely due to the fact that genetics and pure luck, which factor heavily into how long you live, are far out of our control.

“You just can’t exercise your way to living to 100, let alone to the world-record-breaking 122 or something like that,” Dr. Andrew Steele, longevity scientist and author of Ageless: The New Science of Getting Older Without Getting Old, told Fortune. “No amount of diet or exercise is gonna get you that magical combination of genes.”

Dan Buettner, longevity expert and founder of Blue Zones LLC, which studies places around the world where people live the longest, tells Fortune that Johnson is “a walking experiment” and “worth paying attention to.” But it will take notable results a decade from now to really cause intrigue, he says. 

“I applaud anybody who’s tried to use science to live longer…eventually, there’s going to be an intervention that’s going to represent a big leap in life expectancy,” he says. “I don’t think it’s here yet.” 

Most important, Buettner says, is that anything worth making a difference must be adhered to over a long time, and Johnson’s routine seems unsustainable. 

“Most of what he does requires such heroic discipline and presence of mind that fewer than 2% of Americans have the follow through on that, and I feel I’ve questioned even if he does,” Buettner says. “His regimen is so time-consuming and so difficult.”

In Buettner’s research, it’s been made undeniably clear that socialization and purpose ground the people who live the longest. 

“Purpose and…social connectivity are accessible to all of us,” he says.

Living longer also means enjoying how you get there. 

“The same things that will get us to age 100 are things that make the journey enjoyable,” Buettner says.