Hey im 15 i want to start training the gym near me has classes in Kickboxing, and BJJ also submission wrestling and adult MMA but im not old enough yet. anyways my friend was telling me all this stuuf he did saying hehad to break a bone in his foot so it grows back stronger and they hit him in the legs to build "immunity" to being hit with kicks. anyways he said i should start with muay thai and jiu jitsu. i just really wanna do this and turn it into sport. and help/advice appreciated.