I have been there and I know at your age you want to get big and strong fast. I began using steroids at 18. Yes full blown cycles, test, deca, anadrol. You name it I did it and man did I get results. I also got my door kicked in by the drug task force. I know you are asking about ph and not roids, but I said all that to say this. I have not used in 6 years. And this is the part you will probably hate to hear, but with hard work and good diet I am stronger and faster than when I was juicing. I did not know back then about shutdown, actually I did not even care if someone would have told me. I knew it would stop me from getting any taller but that was all I knew. I can only wish now that I did not use at a young age because all I can wonder is how it affected my natural gains and body from what it could have gotten to naturally but never will cause of my decision back then. If all your friends are doing it then they are gonna get bigger and stronger faster than you, but if you will eat right and train like a beast, when you get in your mid to late 20's you will far surpass your friends, trust me.