Whoa! Don't jump the gun too soon! It's ok to be eager, but don't limit yourself so early. You've still got a LOT of school to do (which means a LOT of interests could change with the classes you take and the activities you get involved in) and you should really wait to make a decision that big until you really know that you for sure want to do it. You'll also want to look into schools that aren't just good at theater. You'll want a school that's well-rounded so, if you DO change your mind, you won't have to transfer or anything.
I thought, for five years, that I wanted to be a nurse. One semester into classes, I hated it and changed my major. Since then, I've officially changed it one more time and unofficially changed it about ten times. Most people can't even make up their minds while they're in college, let alone do it five years in advance. I'm not saying it's not possible, at all, but it's just not probable that, at such a young age, you'll want to do the exact same thing later on.
Also, what kind of an actress do you want to be? The theater type that does acting on a stage or the movie type that acts in front of the camera? What about working backstage? Does that interest you at all? Or is it strictly acting? What kind of experience in acting do you actually have? There are colleges that specialize in different areas and it's tough to give you any help without knowing specifics.