Well, you are a bit young. If I were you, I would start doing body weight exercises. Such as pushups, crunches, dips, pullups. Things of that nature. Also start running before breakfast. I would run about 3 miles in the morning and then do as many pullups, crunches, dips, and pushups as possible. Make sure to rest properly too.
I started lifting in 8th grade and never saw negatives from it, so did most of my friends. To the topic starter, read the link wukka posted and learn proper form, keep a good diet, and you'll be fine. Just dont go lifting world records before you learn how to lift.
I heartily accept the motto, "That government is best which governs least"; and I should like to see it acted up to more rapidly and systematically.