Ditto to the others saying the same problem...I had that issue at your age.
Just keep writing, and analyzing what you wrote. Also, take books or stories you like...and books you DISlike...and analyze them. What do you like about them? What do you dislike? Analyze and learn from them. You'll start to pick up the nuts and bolts of storytelling...as well as writing...as you go along. I did this at your age with Anne McCaffrey and Terry Goodkind, because I liked both of their works so much.
It may be a few years before you're in a position to finish a piece...or maybe not, who knows.
In my case, I started writing when I was 10 or 11. When I was 19, I could do the technical stuff...sentences, dialogue, spelling, etc...but I was really really frustrated that I didn't have the experience to write scenes as I wanted them to be. They weren't good enough, because I knew there were some things I just wasn't understanding yet. Not the nuts-and-bolts things, but about storytelling itself, and how to enrich things with my own experience. So even after 9 years of writing, CONTINUALLY, I didn't finish anything, because my skill wasn't up to doing the job as I wanted it to be done. Now I'm 24, and finally on the road to completing a novel, because for the first time I feel as if I have the knowledge and experience to pull it off. So it's possible it could take a while. But...keep writing, even if you don't finish anything. Re-write. Edit. Keep playing with stuff; sooner or later, if you're well and truly persistent, the pieces will fall together as they have for me.
I'd look for other folks in your school who write, although there's unlikely to be very many people in your school that write stories; I took a creative writing class in high school, in my senior year, and out of my entire class, only three of us wrote stories. Everyone else? Poetry, and not too serious about it either. I think I was the only novelist. So I'd look for other folks who do it, but you probably won't find a huge crowd. Might just want to keep your ear in on writing forums like this one, or other writing communities online, to compensate if you don't find many people in real life.
Also...I'm somewhat old-school, I didn't come online until I was 17 and I'd already been writing my own original fic before then for years...but some people find writing fanfic and sticking it on fanfiction.net or some other place really helps them out, because it takes some of the work out of it. The world, and often characters, are already there. You need to provide the plot, the narration and description, and the characterization. You don't need to do the heavy lifting of creating a character from scratch, or worldbuilding or creating your rules of magic or whatever. This doesn't work for all people, but it works for some, and the chance of having people review your work (fanfiction, even bad fanfic, gets far more comments and attention than original work online does unless it's spectacular original fic) can be a goad to write more for some people. I know one Harry Potter fanfic writer in particular who is now edging into pro, since she's sold her first original novel recently. I also know of a pro writer who used to write Xena fanfic. So you might want to explore this avenue, to see if it suits you or not.
