Someone just asked in a comment whether I represent minors, and as I can't find which post that's on, I figured I might as well reply about it.
Yes, I represent minors.
In fact, I currently represent a lovely teenager whose name is Tori Borland, and she's currently working on revisions of a fantasy novel for me. See my clients page for more details about her; she's an interesting person. =)
In general, I have nothing against representing minors. I think teenagers can be just as good writers as adults, and in some cases, better writers. But I will put in the strong caveat that many teenagers aren't great writers... YET.
By and large, when you're a teenager, you don't have the life experience to write a good novel. You also don't have the writing chops to do it. There are rare exceptions to the rule, but most teenagers are working through beginning writing issues while they're still minors. I wrote a ton when I was a teenager, including the first 40,000 words of a novel, but it was utter crap.
Most of what you write as a teenager will be utter crap; it's the simple truth.
But that doesn't mean you should stop writing because every bit of practice you get is going to help you later on. The first novel you write won't be a good one, but the sixth or seventh novel you write might just be the one that finds you an agent. And in the meantime, write novels. Send them to agents. Write short stories. Send those to magazines. Collect rejections, while you get better. I got my first one from F&SF at the age of sixteen. =)