I'm a rock musician. Technically I am a composer, but rock is generally pretty different from what most people imagine for composing. It's very different from classical music, film scoring, and a lot of video game music.
Anyway, my recommendation is to get to school as fast as possible, but it has to be the right school. If you don't already know how to compose it's very difficult to figure out on your own (I somewhat did and it took well over a decade). I took quite a few courses at the local small town community college as far back as high school. I'm not sure they helped me much at all. I think good music teachers are few and far between and you are wasting time with those that aren't, for the most part.
Contrast that with quite a few classes I took with Berklee on-line and it was night and day different. Everything I learned from Berklee was valuable. But they are considered probably the top "rock" music school in the world by many. And it wasn't cheap.
But a good school can make all the difference. That and practice, practice, practice.
One other thing I should mention is that most music programs expect you to already know how to play at least one instrument well, if not how to compose. Their attitude seems often to be "You should have learned music before you got here; we're only here to make you better." You need to find a program that takes you from where you are, even if that's at the very beginning, but it takes at least a few years to get from just starting out to where they expect you to be under the best of circumstances. Reality is, the vast majority of people entering music school have been doing it since they were a kid and actually are competent musicians, if not composers from day one. But with good teachers, you should be able to reach the basic competency expected for a composer in a few years of VERY hard work. (I'm not implying anything about your skill, just pointing out that some people are at the very beginning of the process.)
