I grew up around appaloosas, so that's what I've grown up showing. We have taken some time off at various points along the way, but we always come back to it. When I was 13, I got my first "very own" show horse at the National Show sale in July. At the end of the show season, I was the 4th place rookie of the year. At that point I only did showmanship, horsemanship, pleasure, trail, western riding, and games. Eventually, I got into HUS and hunt seat eq, as well as reining. I've done a little team penning (which I thought was a blast), I've tried rope race and heritage.
One of my very good friends in the show world got his start when he was 64, so 16 doesn't sound so old to me :) And yes, you probably will choke a time or ten when you're starting out, everybody does. Sometimes I still do. But it helps to develop strategies for remembering those patterns! I had a judge ask me after a show was over one time if I was upset that they kept changing the patterns on me. I think I blew three out of four that time, but I just laughed right along with him. With experience comes wisdom, and if you want to show, you'll need a healthy sense of humor in order to handle all that experience.
Learning never stops