It's never too late! However, the people I know that started riding as adults do seem to have a harder time learning as quickly or easily. I think that has to do with a child's mindset. Most kids don't care about what they look like, so there's no hesitation, and often they have no fear. They just ride, and learn by doing. Adults tend to hold back and try to do it "just right" and don't learn as much by experience. So that might be where people are getting their info from when they say "it's too late"--but that's just because they'd be scared to start :). I was riding before I could walk, but I have friends who didn't start until they were adults.
That being said, you're young, so that doesn't really apply to you :). And everyone learns at different rates. And even if you're the slowest learner in the world, it's never too late to learn something new, especially something as fun and rewarding as riding. That's what lessons are for...learning. Doesn't matter what age. Being a former gymnast and dancer will probably give you an edge. You already know how to work hard, your body is already strong, and you probably have natural balance and gracefulness (which is helpful!).