He should take some hours with an approved psychologist.

If you're so into youth, then the next wrinkle will be your happiness' end. That one grey hair will start some "omg omg omg".

So, can a human be happy always pursue his youth? Should be the first question to answer.

What about the supplements? Recently done studies showed supplements do not really have an impact. They also can be dangerous in cases of fat soluble vitamins & minerals. That ones get stored in our fatty tissue (if we high or overdose them). Like vit D - in the beginning, not a problem. Storage of it in fatty tissue, also not a problem. The problem begins with satisfying the bodies' need of vit D and still take in high doses. At certain point, we may've taken to much and see adverse effects. But, just stopping taking won't do it. The vit D will be slowly released from the fatty tissue keeping the levels still high. That can happen with all the supplements having fat soluble vitamins and minerals.
The other thing is, most positive studies are conducted on behalf of the supplement producer. So they're all positive. Independent studies, on the other hand, show "no use. Even possible harms". So desperate pursue a healthy body may turn adverse.

That plasma exchange may have some usage. As it's also already known, our immune system is not just fighting gems and stuff. It is also our fire extinguisher and the cell repair guy and may introduce or fight cancer as well (always trying to fight bad guys, it can misrecognize and fight own tissue leading to always inflamed tissue parts. Some cells can mutate unadvantageliously and not being recognized by the immune system as bad cells anymore, they can grow to cancerous tissue. What is also known, our immune cells become lazier the older the immune system is. In my late 30ies, I'd catch a cold every two weeks with herpes on the lips and general bad shape. My immune system has seen quite a lot of antibiotics taken over the years by then. Then, a serious condition made it necessary to have some blood transplants and also an ileo stoma (exit of the colon through the stomach). 8 weeks long my colon parts after the exit did not see a THING. No food. No fluid. Nothing went into the lower bowels. Nice side effect: i saved so much of toilet water these days, unbelievable. After the exit has been closed again, I did not have any cold, no cough - nothing! - since. For now more than 10y. Even when I try to get ill - nothing! I'm still in a serious condition and belong to the peer group of the most vulnerable in that hindsight. But I'm "healthier" than the average Joe. And in terms of respiratory diseases, I'm healthier that the most healthiest men hahaha

So exchange of the blood plasma also spills "fresh", "young" and not so experienced cells into the old body. As I reconsider, the youngest gives his blood to his father, father gives his blood to his even older father.

It's also about the gut bacteria. Microbiom. That's actually is the reason we have an immune system, because our immune cells get stimulated to recognize good vs bad... and so on... So, taking this thinking into account, a diet would help to change the composition of the microbion which by itself influences the immune system.

Other thing to consider.. that guy pays a lot of care for his body. It also may be the good skin care and the workouts that make him look younger.
I also started to pay more attention to my facial skin. Means, everyday cleaning with soft cleaners, using some fruity acid peeling cream, and applying a lot of expensive creams twice a day. Nothing special is noticed by me, but I got questions like "you look so fresh and healthy. What have you done?"

So. I think there's a lot of correlation. Some things he does like plasma exchange may belong to causation. But most will be correlation effects.

If you want to stay young, eat less and healthy with low sugar, salt and artificial sweeteners or other artificial ingredients. Cook everything yourself. Check the amount of energy, as everything we intake will result in "waste" that may have some adverse effects if not transported out the body by urination and s*itting. Take example on the oldest people of the world, the Japanese elders. They never have had a prosperity in terms of life and food and so did eat less but good with every substantials the body needs (fat fish, good protein, less red/white meat, vegetables and in general less food processing like cooking with high heat, grilling and whatever is done to prepare a meal. And, the amounts have been right enough not to get starved. We're talking like 100y back in time. Just imagine their life at that time)