There is learning music, then there is learning music in college. People assume that since their band is the hit-show around town, that they have a guarantee spot in a college music school. They would be wrong. Here's what I myself am doing, and what some peers of mine are doing as well.
Last summer, my cousin auditioned for a spot at the University of Colorado Music School. He unfortunately didn't make it. I was talking it over with him, and he was telling me what he did wrong and what I should do if I chose to study music in college.
My guitar teacher, a graduate of the University of Tennessee at the Clemson Music Program once gave me a list of the things that were on his first semester year syllabus. While I can't find it now, talking with my cousin, my teacher, and friends who are considering music as a profession, I have developed a list of key and critical things that will increase your chance at a spot on the musical program of your college of choice.
Ideally, you, the reader, are a 14 year old child entering high school. You have 4 years of solid guitar under your belt and you can maintain a band and have a basic knowledge of music. Many high schools offer a multitude of music classes, ranging from performance to technical to perhaps business. Your best bet is to see about joining the marching band or concert band while also taking another class (if its possible) such as choir or steel drums.
When it is available (if it is), see about trying to get into a music theory class/music history class and take advantage of your school's jazz band. If your school offers things like teaching to younger kids at the middle school, or sponsors extra-curricular activities relating to music/summer camps/(summer) clinics/workshops, whatever. Drop by your band teacher's office one day to chit-chat with him about opportunities such as the ones I listed.
Meet, talk, meet, talk, meet, and talk with as many people who play music professionally as you can. The more experience you have around these people the more you will be prepared for not only music in college, but as a profession.
Now, as far as the technical side of things, this is based off of a syllabus my guitar teacher gave me. This is the stuff that you may or may not be auditioning for, depending on the school.)
Be able to know and..
Play all your major scales. (All 5 positions of them in the CAGED format)
Play all your minor scales. (All 5 positions in the CAGED format)
Play all your modes of major. (All 5 positions in the CAGED format)
Play all your modes of minor. (All 5 positions in the CAGED format)
Play all your diatonic majors, minors, half-diminished, and diminished chords. (And by that, I mean your 7s)
Play a wide number of scales such as: chromatic, whole tone, pentatonic, blues, altered diatonics, diminished scale and be able to play them in all CAGED forms (if applicable).
Be able to quickly make and extend chords (i.e: adding 9s, 11s, 13s etc.)
Be fluent in your theory (harmonization, triads, diatonics, rhythm, scales, etc.) Know how to sing (not beautifully, but able to hold a melody)
Learn How To Play The Piano (and by play, I mean be able to sit down and sight-read any moderately challenging piece of music)
Be able to sight-read: a jazz lead sheet, a classical piece, and anything else you can think of. (Know the terms, i.e: head, lead, melody, solo, outro)
Be well versed in your jazz (as in, know dozens of songs and be able to throw a chord-by-chord improvisation solo on the spot)
Be well versed in classical music (including the history, types of classical music (Renaissance, Baroque, Neo-classical, what have you.) and be able to play a variety of styles of classical.
Now every school is different, so you may or may not be playing that. Especially if your going into something along the lines of music business or recording. But as far as performance goes, that is what you need.
Realize, that rock and roll isn't really catered to that much in college. Jazz and classical are primary focuses. This means that you need to be able to expand your musical horizons and find some classical and jazz you like.
Keep in mind that this is a rough guide and each school has something that I haven't included. Contact the school your considering and see if they can give you some advice on what you need to prepare for.
Studying music in college is something that takes extreme practice and patience. You can't pull it out of your ass, it has to come from years of study, and even then your not guaranteed. Take this guide for what it is, a guide.