My 9 year old bird is scratching his butt?

My 9 year old cockatiel does this thing where he sits on his cage and rubs his butt back and forth and the edge of his cage. He just started doing it about a month ago. I'm concerned because Its all he does all day long and If you come near him while he's doing it, he will charge at you and try to bite you and he become very territorial.Is this normal behavior? I've tried to get him to play with his other toys but he doesn't. Do you have any suggestions of toys that I could buy for him that he might like?