Tech CEO Bryan Johnson’s rigid routine of 1,977 vegan-based calories a day, a couple dozen morning supplements, and consistent organ testing caught the attention of the masses ever since he first shared his reverse-aging protocol with Bloomberg in January. The 45-year-old’s quest for immortality has garnered massive criticism from longevity experts and doctors who question whether his dedication will prove anything long term, not to mention the impact it may have on his quality of life.

Pulling the strings behind Johnson’s reportedly $2 million longevity craze is a team of 30-plus doctors and health experts, led by 29-year-old Oliver Zolman—a millennial doctor obsessed with turning back the clock.

“I’m going for results that have never been achieved ever,” Zolman tells Fortune. “My bar is very high.” Zolman juggles about 10 clients at a time and reportedly charges upwards of $1,000 an hour for intensive age-related testing, according to Bloomberg’s profile. Zolman did not share his current rate with Fortune, but says he charges people based on their net worth. "

“If they have no money, then I just don’t charge,” he says. “If they’re a billionaire, then it’s like, ‘Okay, thousands of dollars is nothing to them.’” Still, Zolman says most of his clients are similar to “Bryan’s demographic,” with some exceptions. But in a follow-up email, Zolman said he does not charge anyone except for Johnson and “never actually charged $1,000 an hour.”

Zolman, who lives in Cambridge, England (but also spends time in Spain and hopes to open a clinic there), introduced himself as a “professional evidence-based rejuvenation coach and clinician trainer” at a lecture during the Longevity Summit Dublin last year.

“Rejuvenation just means getting younger, or making it younger so obviously to prove that, in an evidence-based way, you have to measure the age of something,” he says, adding that he measures individual ages of organs to determine protocols for clients. “You can’t just randomly say I feel younger. That’s completely ridiculous.”

Zolman has been fascinated with longevity and regenerative medicine—modalities that aim to combat age-related changes—since he was young.

“I learnt about growing new ears on the side of mice, and making frogs grow eyes in their stomachs, or just 3D-printing replacement organs,” Zolman told the Times U.K. earlier this year, which reported he was raised by a father who is a museum manager and mother who is a ballerina and ballet teacher. “It seemed kind of like a video game.”

Injuring himself while playing basketball during his first year of medical school at King’s College London propelled him further into the longevity field, per Bloomberg. After struggling to walk for a year despite working with doctors, he took matters into his own hands and treated himself through physical therapy. He later graduated with a degree in regenerative medicine and biology. He is now creating a curriculum for a longevity school for doctors looking to branch into regenerative medicine while working in his Cambridge lab, and of course, with Johnson as part of Project Blueprint, which encompasses over 200 longevity-related protocols to help reverse biological age. For Zolman, it’s always been about innovation. The pace of science is too slow for him, he says.

“Gene therapies and cell therapies are coming through in the next 10 years, and it’s just going to continue to get better and easier and less expensive and less effort for the individual to do,” he says, adding he is aware of his critics who point out that Johnson’s longevity quest isn’t accessible for most people. “Eventually, you’ll probably just have a load of gene therapies or things that mimic gene therapies in some clever way,” he says. In a talk hosted by the Oxford Society of Ageing and Longevity, Zolman said thousands of randomized trials in the queue will inevitably grow the field of longevity research, especially as more people like Johnson serve as guinea pigs.

Zolman currently spends a large portion of his day combing through medical studies and journals, posing questions to experts, and working with clients on their longevity protocols. In whatever free time is left, he plays tennis, basketball, and the bass guitar.

Zolman’s longevity protocol

Zolman’s longevity goal is no easy feat. By 2030, he aims to discover how to reverse the age of each of the 78 organs encompassing both genders by 25%. As of January, Zolman told Bloomberg that despite Johnson’s determination, “We have not achieved any remarkable results.”

He added: “In Bryan, we have achieved small, reasonable results, and it’s to be expected.” He admits he still hasn’t gotten to the point with Johnson to call the results “remarkable,” but there’s been progress.

“We have some new results coming out soon, but we’re still analyzing them on the thymus,” he tells Fortune. “So I might have rejuvenated his thymus…if I rejuvenate Brian’s thymus by like two decades, for example, then that would be a remarkable goal.” Zolman is also focusing on rejuvenating Bryan’s lungs, which were majorly impacted by COVID-19. He’s added swimming to Johnson’s protocol as a result.

The protocol is twofold: measurements and therapies. First, instead of measuring someone’s aging by common modalities such as VO2 max alone (the maximum amount of oxygen the body can use during exercise), he focuses on measuring all 78 human organs to determine which ones are most in need of his therapies.

“You want to be addressing aging from every angle that we have available,” he said at the conference. "

Using these measurements, Zolman goes to the next phase, the therapies. “You try and get all the markers below chronological age,” Zolman continued. “If your markers are older and more clinically relevant, then you want to target those organs first.”

Johnson says his work with Zolman helped slow his pace of aging by 31 years, according to the Project Blueprint website.

Zolman’s approach has three levels, the first being the least invasive and mainly consisting of changes in lifestyle factors aimed at extending people’s health span and life span. Level 2 consists of non-age-related modalities, while Level 3—where Johnson sits—contains organ rejuvenation protocols aimed at fully reversing aging (he has reportedly received blood from his 17-year-old son, although there were no benefits).

Zolman and Johnson seem to crave the gamifying nature of rejuvenation and reverse aging. It’s what led the duo to spearhead the Rejuvenation Olympics, which ranks people’s biological age on a leaderboard when they adhere to certain reverse-aging protocols, like Johnson’s blueprint. Of course, Johnson tops the list. Zolman also abides by similar protocols in level 1 and shares his results on the leaderboard. (He says because of his age he doesn’t need to abide by the rigid protocols of level 3.)

“I love competition, and turning rejuvenation into a scientifically valid competition is very exciting,” Zolman said at Longevity Summit Dublin. “Longevity school can help you do this safely.”

In 10 years, Zolman hopes all of Johnson’s organs will biologically reach age 50 (he will be 56).

“It’d be nice to be 10% younger than his chronological age in all organs,” Zolman says.

Johnson, who reportedly speaks on the phone with Zolman for about an hour daily, isn’t slowing down anytime soon.

Standing up in the face of critics

As the obsession to live longer continues, the research speaks for itself. Getting outdoors, moving (even a quick walk), eating a nutritious diet, sleeping well, and maintaining strong social connections can help us live longer and stay healthier while doing so. And due to epigenetics playing a role as a hallmark of aging, Moshe Szyf, professor in the department of pharmacology and therapeutics at McGill University and founder of biotech company HKG EpiTherapeutics, says changes in lifestyle could indeed reverse aging. Still, he is cautious about Zolman and Johnson’s approach.

“It is unclear, however, whether we have yet the knowledge on how to do this. It seems that Bryan Johnson is applying a tour de force of anything suggested to affect longevity and uses a barrage of tests to examine functional changes,” he writes in a statement to Fortune. “It is also clear that changes need to be personalized.”

Genetics also play an integral role in how we age. It’s a factor for identifying the so-called SuperAgers of the world—those in their eighties with brain capacity akin to those 20 to 30 years younger.

“No amount of diet or exercise is gonna get you that magical combination of genes,” Andrew Steele, Ph.D., longevity scientist and author of Ageless: The New Science of Getting Older Without Getting Old, previously told Fortune. "

It will take 10 years to see if Johnson’s protocol really turns back the clock, longevity expert Dan Buettner, who studies the lifestyles of the world’s centenarians—those who live to 100 and beyond—previously told Fortune. After all, Johnson is “a walking experiment,” Buettner said, because no one has gone through this level of rigorous habits and testing in front of a national audience before.

And while the critics question the validity behind Zolman’s rigid longevity approaches, Zolman says he prides himself on the rigorous safety testing of his endeavors. “The stupidest thing in the world…is to die from an experimental longevity therapy,” he said in Dublin.

And to those who question him, he has a simple response.

“No one’s gray hair reverses randomly,” he tells Fortune. “Everything’s an experiment in medicine. That’s what’s called practicing medicine.”

And for those fascinated by Zolman’s approach, it underscores another important factor in the race for longevity: The game to live longer is also deeply fueled by the amount of money you can invest to get there.