Everything has a target audience. With the exception of really, really old people, though, there's stuff been made for everyone. The real question isn't whether anime's too young for a person, it's whether that person's even suited to anime-- at least, any one anime.
I don't think so. I'm 21 and started enjoying seven years ago. No sign of letting up, fortunately. blaugh The only age there is are age restrictions, but there are ways of getting around that one.
There is no age for watching anime. Because no matter how old or how young you are, there will always be things worst. You should watch what you want to. Unless it's like, porn.
Outside of Hentai, no, there's no age for Anime. Honestly, I'll never tire of Card Captor Sakura or Sailor Moon. ^_^ And let's not forget Rurouni Kenshin.