I started gymnastics when I was 12. I did rec and then joined the high school team. I grew up outside of Milwaukee, and there are lots of high schools in the area with gymnastics. It's a great way to do gymnastics with people your own age and skill level. I was never very good, but it didn't matter. I loved what I was doing. I now do adult open gyms for fun, and I've done a lot of coaching and recently started judging. I'm a much better coach and judge than I ever was a gymnast.
The thing that helped me was to remember that I was never going to be as good as the kids who started when they were six. I was in it for myself, and I was my own competition. As long as I was improving and having fun, I was happy. I never compared my scores or skills to other gymnasts because I would have lost every time.
Salto has a class for high school gymnasts in the summers - you may want to check it out in preparation for high school if you do decide to go in that direction. Also, if you want to do high school, maybe talk to a high school coach to decide what skills to work on - it's very different than USAG. Or feel free to PM me.