It seems that if you want to remain forever young, you don't need the Fountain of Youth, but rather to choose the right profession. Whether it is a negatively or positively spun article, every single one focusing on Paul Ryan refers to him with some sort of youth-oriented verbs- "boyish and young" being the main two. He is 42 years old. Imagine if he were in a different profession- underwear model, perhaps (many wish he were!). He would be considered well past his prime. Same with Julio Castro, the youngest governor of Texas at age 37. President Obama himself joked that he looked more like an intern.
On the other end of the aging spectrum are gymnasts, particularly in the Olympics. How old are you? 16? Psh, far past your expiration date. Gymnasts peak around age 14 or 15, when China tries to sneak them into the Olympic Games.
To stay on a continuous path of youth, here is what I recommend: become a child actor, then a gymnast, then a model, then a politician. Boom. If you follow that list of occupations, you will surely remain forever young.