Well, you mentioned "growing pains" in your post title, but I don't believe that you're having actual bone growth at all at your age. Are you working out heavily? Because unless you are, I don't think that you would experience pain from intense gains in muscle. I have heard that T can make you more susceptible to joint and tendon injuries, but I don't know what the mechanics are behind that. I haven't experienced this myself, but others may have.