The mega rich California CEO follows a strict diet, sleep wind down ritual, exercise regimen, takes a round of daily supplements, and undergoes countless medical tests as he strives for the biological age of 18. Johnson is estimated to spend over $2 million this year on medical tests and various procedures aimed to help him achieve his goal, according to a profile of his endeavors in Bloomberg. 

Johnson’s intrigue with longevity science has left us all wondering: will all of this really be worth it? 

Dr. Andrew Steele, longevity scientist and author of Ageless: The New Science of Getting Older Without Getting Old, says it’s an exciting time for research on aging and longevity medicine so people can live longer, and more importantly, healthier lives. But in the case of Johnson, he says science has not confirmed all of his strict approaches. 

“The real challenge is that we just haven’t got anything that I would confidently recommend that can slow down the aging process beyond the obvious stuff of diet and exercise,” he tells Fortune. “It’s quite likely that a huge fraction of whatever effect he’s seeing is just the fact that he’s got this incredibly strict exercise regime. He’s eating more nuts and vegetables and most of the stuff that’s in his diet is an improvement.” 

So with Johnson’s strict regimen, how long could he live? 

Steele says putting a number on it is impossible. First, because Johnson has dedicated his life to adhering to various approaches simultaneously, it will be difficult to understand which modalities, if any, really made the difference. 

“It’s really hard to disentangle, is it some exact combination of supplements he’s taking? Or is it 90% of the effective stuff that you can do without $2 million a year?” he says. 

Secondly, because, unfortunately to some, we cannot control everything. While a bulk of living longer and avoiding debilitating chronic illnesses lies in lifestyle changes, another factor is genetics, and the other is mere luck. 

Dr. Shoshana Ungerleider, an internal medicine physician in San Francisco and the founder of End Well, a non-profit focused on reframing the end of life, says while monitoring lifestyle factors is key to aging well, and lowering the risk for developing chronic diseases that present more frequently with aging, genetics still play a role. 

“As much as we would like to be able to control our fate, it’s just not possible. Many of us carry genes that can undo all of our best intentions,” Ungerleider says. 

Further, the human body is not meant to live well past 100, and even research on centenarians show there is a strong genetic factor to their long fate, Steele says.  

“You just can’t exercise your way to living to 100, let alone to the world record breaking 122 or something like that,” he says. “No amount of diet or exercise is gonna get you that magical combination of genes.”

Ungerleider also urges people to focus on quality over quantity. 

“Our time is the only thing we can’t get back or buy more of,” she says. “From my experiences caring for many patients at the end of their lives, it’s not about the number of years lived, it’s about the quality of that life…In the case of Mr. Johnson, it is difficult to predict whether these extreme measures will significantly extend his life expectancy. Given how strictly he has to adhere to nutrition, exercise, medical testing, and so forth, I am concerned that his quality of life is compromised.” 

While she doesn’t see it as reverse aging per se, there are steps people can take to slow aging and help prevent illness. These include limiting alcohol consumption, avoiding highly processed foods, moving your body regularly, maintaining social connections, and prioritizing stress management, she says. 

A gold standard to beat is 118—the age of a nun who lived in the south of France and became the world’s oldest known human last year, according to a statement from the Guinness World Records. She died in January.

Sister André regularly indulged in chocolate and a glass of wine each day, her nursing home confirmed to CNN in April. 

If Johnson does indeed reach André’s age—spending that $2 million a year up until the end—reverse aging would have cost him nearly $150 million. Steele and Ungerleider hope people instead see that there are accessible ways to control some of life’s potential health outcomes without having to cash a check. 

“This lifestyle is not feasible for the average person, meaning that these interventions are not possible at scale,” Ungerleider says. “These measures are expensive financially, physically and psychologically. Additionally, even if there is proven benefit, the majority of people are not able (or interested) in dedicating every waking hour to preventing aging.”