I agree that he he was taken away before he learned what “too hard” was. I’d try giving him a wiffle ball or a foot toy he can play with. That part doesn’t sound like aggressive behavior. As for the cage aggression, we adopted a green cheek the year before last (she was 9 at the time) she was extremely aggressive and bit the snot out of me several times. She would do it mainly when I went to get her out of the cage. So when she bit me, I would calmly take my hand away, shut the cage door and walk away. A few times of this and rewarding her when she didn’t bite, and it’s now a year and a half later and I haven’t been bitten since. She doesn’t like to be touched except on her terms, but she no longer bites when I take her out. And since I let her wings grow out to where she can fly, she’s a much happier and healthier bird.
I dont think it’s really so much aggression as it is testing boundaries but not knowing how hard with his beak. Try calmly walking away, meaning no words when he bites hard. You’re gonna get bit fixing it. The first time that he comes out of his cage without biting, reward him with a treat. Mine usually work for safflower seeds, a piece of millet, Avicake or nutriberry.
