Age is just a number. I'm a proud 33 year old, who doesn't feel a day over 16. Luckily I don't think like a 16 year old because I don't want to think like I teenager. I teach high school kids and the things they think...lol. Always makes me ponder, if I acted that way at their age.
I don't think age matters in reading and writing fan fiction. If you enjoy it, that's all that matters.