IMO, proper nutrition is half the battle. Your friends will get bigger until they hit a wall. If they ate more they would have more potential. On the other hand, if your protein intake is up, along with all the other essential vitamins & nutrients, the wall will only come due to an overused routine.. Which is easy to correct, a good diet must be made a habbit of (not so easy)
and BTW, most everyone has a jump in the begining of strength and size.. it's what you do AFTER to jump that counts..