If you want to risk killing someone or seriously injuring their brain, then yes -- aim for the back of the head where the brain stem is most exposed. :blink:
Sounds to me like the OPs 16 yr old son is getting picked on by bullies. Eye gouging, ball kicking, and hitting in the back of the head probably makes sense if he fears for his life. If its just getting picked on by a bully at school, i'd say best to do is make fun of the bully (in a way that he's embarassed to pick on you) and/or just stand up for yourself. Punch him in the nose.
Most bullies like to pick on people who won't push back.
Kicking people in the balls and gouging eyes is a one way trip to being made fun of even more.