I was in Civil Air Patrol when I was your age...
Its a part of the US Air Force that has a cadet program (ages 13 to 21 if I remember right) which specializes in aerospace education, leadership, and search&rescue/emergency services. Its pretty cool...meets once a week usually for a few hours, where you learn about the military, airplanes, and other things like that. Then you'll probably go on field trips (my favorite one was when we went to the United simulators in Denver and I logged 747 sim time). They give you a few free flights as well as greatly reduced priced training (I don't know much about that though...I didn't fly with CAP). You can also use CAP as a building block for college applications and things like that.
If you're into the military and airplanes...find out when your local squadron is having a meeting and stop by. They'll me more than happy to let ya watch what they do and answer any questions for you.