You asked for a genre and a minimum length--not all that specific. I think that the people who are trying to help you have the right to ask for clarification on what you want to see.
Personally, I don't particularly recommend self-publishing unless you're going for a small target audience. From your own writing sample, I'm guessing you're going to write a vampire novel--not exactly a niche market, given the success of Anne Rice and Stephanie Meyer. If you just want the satisfaction of being in print, perhaps just order a few copies. If you can't get published by a publishing house, the odds are against your making much profit.
I can think of two teenage authors off the top of my head: Amelia Atwater-Rhodes and Christopher Paolini. Atwater-Rhodes's earlier books were okay, though they were fun reads, and she's definitely gotten better. I've only read Eragon of Paolini's series, and that has gotten very, very mixed reviews. I thought it was a decent book, if somewhat irritating on a few points.
The two had something in common: connections to the publishing world.
Atwater-Rhodes had a teacher who was a literary agent.
Paolini's parents had a small publishing press, if memory serves, and they printed Eragon themselves before a larger press picked it up.
You aren't as good now as you'll be in a few more years, when your skill really matures. You should write it now, if only for practice, but don't necessarily publish it. You'll still be able to say that you'd written a novel when you were thirteen. You'll be able to look back on it in a few years, and you'll likely be astonished at how much you've improved since then. I know I am when I look back at some of the older things I've written.
Maybe try posting it on a site like Fictionpress: it's free, and it might be a good way to get some feedback on your writing. Alternately, you could ask some people around here to look it over--I'm sure plenty of people would be happy to help you out.
Your goal is an admirable one--I didn't write anything particularly long until I participated in NaNoWriMo last November. Even that was pretty darn crappy, and I'm too scared to go back and edit XD. (In my defense, the goal of NaNo is getting the word count down and worrying about revising later.) If you really feel like publishing now is right for you, then go ahead. Just don't expect to be a smashing success. It's possible, but not very likely.
Make sure you're careful about picking a self-publisher--some are good, but many are not. I've heard Lulu's a good choice, but I've not used it myself.
Good luck with your novel!