The response he gives may vary whether he's talking to a peer or an adult. Peers may do it to taunt him (since it is the obvious trait they can focus on) He can let others know that he is well aware of himself both physically and in regard to his inner qualities (What he is good at, moral/spiritual abilities, etc)
When someone comments on his hight, he may remind them that genetics shape one's physique. Since he would not be able to prevent others from making comments now or later in life, he himself has to believe that the body is only a "vehicle" It is not the total sum of the individual. You may have him read about men in history who were not tall and yet accomplished many great things. It is the mind behind the body and that is what he can tell others.