Attack the Newspapers!
If you're argumentative and enjoy heated discussions about anything, the essay/op-ed market is one you won't want to miss. It's also a market that you can start getting involved in a little bit at a time: your newspaper is the place to start.
Start a habit of writing a letter to the editor once a week. The smaller the paper, the more likely your letter will appear. Kathy Henderson, in The Young Writer's Guide to Getting Started, comments that many smaller newspapers are understaffed and would love to have a teen reporter or columnist.
If you start small, with responding to articles every week, you can develop a relationship with the editors. They'll appreciate your input. Then, after a while, you can see if there's a spot in the teen section-- or if they would let you start a teen section. Talk about experience!