Back in the second edition of AD&D, potions of Youth and Longevity were valuable, both to GMs as plot devices, and as a useful way for players to compensate for the variety of supernatural effects that caused aging. However, when Third Edition was released, unnatural aging was largely removed as a gameplay mechanic, having been replaced, for the most part, by experience point costs and negative levels. Potions of youth and longevity were removed at the same time, presumably as being no longer needed as a way of balancing powerful spells. (Also, third edition and 3.5 both moved potions away from having effects not covered by spell effects, and Pathfinder both removed the concept of experience point costs and made negative levels much easier to deal with. These aren't obviously relevant to my question, but I mention them here in case they're relevant to someone's answer in a way I can't predict.)
I'm looking to return the flavourful potions of Youth and Longevity to my Pathfinder game... But I'm worried that I might unbalance the game, or severely weaken the vermilisitude of a setting if I make eternal youth too cheap and easy to obtain.
Compounding this is the fact that I've got no actual play experience with second edition, so it's easy for me to misjudge the effect these potions had on the game.
Has anyone attempted to adapt potions of youth and longevity for Pathfinder before? For that matter, are there any published rules for it? What pitfalls should I look out for? How should I go about adapting second edition's Youth and Longevity potions to the Pathfinder rules?