Alicia is spot on. There are a lot of workshops for acting that are designed for younger people.
I'd like to make a plug for trying out Improv Comedy. I see you are in San Jose and I believe there are some great theaters and training centers for Improv comedy in your area. Comedy Sportz has a theater in San Jose, they are very well known and they have a teen program.
Improv will give you essential skills for acting as well as help you to think on your feet (very important for live theater). You will also make a lot of connections in the Improv community; which is excellent networking. Worst case, if you discover it's not for you, the skills they teach in beginner improv are applicable to every day situations with school, work and social interactions.
I'd suggest starting with local theaters - many of them will put on workshops, summer programs and even camps to get you started with an education in theater/acting and also get you experience. If you have someone at school that puts on plays, you could ask them if they know of any programs that might be a good fit for you, too!