I want to study Music Theory and Composure?

i am 15 1/2 years old and i've been playing guitar since i was 10. i'm pretty good at it, but i taught myself how to play and i play by ear, so if someone asked me to play a E Minor scale, i couldn't do it. i've never taken lessons from anyone, and i was just inspired by listening to other music and playing it. i know certain terms such as Arpeggios, Pinch Harmonics, etc. when i graduate from high school, i want to go to college and study music Theory and Composure. is there anything i need to know and accomplish before i go off and get a course in it?