If you're interested in eventing, dressage or show jumping, I highly recommend joining the United States Pony Club if there's one in your area. It's incredibly helpful and fun. Our region's highest rated member (an HA) is a guy, and he's very well-respected. You wouldn't be out of place at all joining Pony Club. The great thing about it is that you can be a member until you're 25, so you won't be booted out at your 18th birthday like a lot of youth clubs.
Just remember that riding is in no way a feminine sport. It is HARD work (just wait until you start working on posting without stirrups....), but very rewarding. Don't be afraid to pursue showing if it interests you!