A 13 year old who's only watched Pokemon?
Well, the obvious choices that you'd probably enjoy at least one or two of are the long running Shounen: Bleach, Naruto, and One Piece- with added Fairy Tail or Soul Eater as you please. Just pick one and go all out.
As for shorter choices, people'll generally point to shows like Cowboy Bebop, more Western appealing anime to get people started, because that does make sense. But I'll recommend Durarara!, Angel Beats!, and Baka and Test to get three particularly different, very anime tastes. And if you like any of those, anime's for you. If you don't, those anime aren't for you.
Bonus, Shirobako. Whether you'll like it's up in the air, but if you're interested in the medium and want some form of appreciation for it, or just love stuff like it (both of which are me), I'd recommend checking it out. Gives a fair deal of insight, and it's one of my favorite shows for that.