you find a ring that lets you live forever. It keeps you eternally young, in perfect health, and at your physical peak. Forever and ever, until you take it off, at which point you start to age normally again (from the age you were reset to) and lose the superhuman perks. there is only one ring.
What do you do?
to clarify, letting someone else try it on would make them eternally young too. If they take it off, they would age normally from the age they were reset to. Think of it as a reset button.