When should i start yoga?

im 12 right now and am pretty flexible. When do you think would be an appropriate age to start? i do not want just to learn small breathing poses i want to become advanced hand balancing and very flexible tricks. I am a gymnast and can do a roundoff back handspring. And how long does it take to become so advanced? thanks! also is there a special diet/menu plan i should follow to help get more flexability? thanks!