Whats wrong with my brother?

Hi im 16, and just started developing , (i know, sad, right), and he is by half-brother, and i live in Austin TX, and he's somewhere in VA so we dont see each other that often. He visited us (btw- he's 11) and last time we saw each other was about 2 years ago, and he noticed my s and keeps touching them and asking to see them! And when i was taking my shower abut a hour ago, he came in and stared at them! And he keeps asking me to show them to him, and its SO ******* ANNOYING! HOW DO I STOP HIM!