How to get a six pack(14 year old Guy)?

Im a 14 yr old boy. Ive been going to the gym 3-4 times a week since February. I use the stair master and bike to help burn calories. I do crunches and the bicycle ab workout, i also do a machine called the ab twister there. i do 120 crunches when i go and 5 sets of the bicycle, Im 5'9 and 149 pounds. im not fat at all, and not really really skinny. Im in good shape, but its not a six pack, its just a flat stomach i guess. I eat kinda healthy but not the best. Please help and give me tips! Is it the food Im eating? or do i need to do more workouts? I REALLY want A SIX PACK!