i would honestly suggest you wait a couple of years. you may not grow taller, but you are still growing. ever notice the difference in the frame of a 6 ft 19 yr old and the frame of a 6 ft 27 yr old? long bones, like the clavicles are still growing. they will determine how wide your shoulders are. AAS can close those growth plates prematurely. believe me. if you focus on diet and training, you can learn to add a lot more mass naturally. then your foundation will be that much better when you do start gear at 21. this is a marathon, not a sprint. in you're in this game for the long haul, you'll be much happier with your long term development.