I started gymnastics when i was 17!!! You're never too old. You might be in a class with younger kids but it's not a big deal. Little kids don't care. I was lucky enough to find a class that only had 2 other girls in it and they were around 13 or 14 so it wasn't like I was with a bunch of 5 year olds.
I need help with this exact same thing.. :( I'm 14 and did a little cheer but I don't want to be around the kids!
You should defiantly try gymnastics! It's a really good sport and it doesn't matter if your not good to start with. Join a recreation class and work your way up.
I think you should have started Gymnastics when you first started dancing but usually if you are a dancer than it's easier to Tumble (Gymnastics) soo I would try it!
If you think that your good at gymnastics then go for it do it and if you put your mind to it then you will feel fantastic.