If he is messing with them a lot and they are all in the areas where his beak can reach, I would say that he is likely barbering and/or plucking (barbering is not the same as plucking, but similar--it's like feather chewing that breaks them bit by bit). Have you had him to the vet for blood-work etc? Sometimes it is behavior-related (or due to boredom/anxiety etc) but other times, they will pluck if in pain. The fact that he is doing it back and front makes me think it's behavioral, but you should see if you can get him to a decent avian vet just to be sure.
That having been said, ****Make sure you are petting on the head and neck only and remove any shadowy spaces from his cage (NO TENTS/HUTS!)****these are hormonal triggers and a sexually frustrated bird will often pluck/barber in many cases. Do not allow access to shadowy spaces outside of the cage either...no cuddles or snuggles...no boxes, drawers, blankets etc. He is at a hormonal age where he is starting to look for a mate.
Make sure he doesn't see you as a mate or he will get frustrated that you are "making promises" you can't keep (as a human).
Also- as an adult or pubescent bird, he will need 10-12 hours of sleep nightly (on a schedule) to help regulate hormone and immune function...So make sure he is sleeping soundly on a schedule for the proper amount of time.
Do you know his sex? If not, I suggest you find out. Female birds can get hormonal and become egg-bound (even if there isn't another bird around) so you would be better off knowing.
