I don’t think a Fountain of Youth would work in zero gravity.
There have been many reports about astronauts not aging or even becoming younger after going to space, and like any sane, logical person, we usually find that hard to believe. However, it may have some truth to it, at least based on various studies performed on astronauts’ bodies before and after going out into orbit.
The phenomenon is called Time Dilation, and it really does exist as a physics principle. Time Dilation states that when something is moving quickly, especially in a low to zero gravity zone, it also ages much slower. Scientifically, it can be defined as the “difference in the elapsed time measured by two observers, either due to a velocity difference relative to each other, or by being differently situated relative to a gravitational field.”
One of the most famous examples is Scott Kelly, a 55-year old astronaut who claimed that he became ‘younger’ than his twin after coming back to Earth a year after his launch. Although not aging may seem like a good thing to some people, for many astronauts, it actually translates to a lot of pain.
In an interview with The Guardian, Kelly listed down the various physical effects that going to space caused him. “Physically there’s stiffness, swelling of my legs, rashes where my skin hasn’t touched anything, nausea.”
“In space you lose a significant amount of blood volume. You regain it when you get back very quickly but what you don’t regain is the red blood cells you lost with it and that takes months to recover. That makes you feel fatigued. It’s a six-to-eight-month recovery. Then there’s things you can’t feel: bone loss, muscle loss, structural changes in my eyes.”
He also adds, “The effects of radiation at a genetic level– I don’t know what they’ll be.”