Open Question: Im 13 and I can't get my abs to show. HELP!!!!?

I am 13 years old, male, 5'9, and 136 pounds. My waist is 29 inches. I have two upper abs, and when I flex you can barely see my four pack, but no 6 pack. I play tennis weekly and I dance every Sunday for 5 hours. I have a mini 9" fitball that I do ab workouts on that. I am not old enough to go to the gym. How can I get my abs to show?? My body fat percent is 11.3 and my bmi is 20.1 The reason why I want abs at such a young age is because it will up my tennis game so I can secure my varsity tennis team spot as a freshman.