It certainly sounds like hormones and maturity may be at play here. When birds are left flighted and can generally come and go as they please, or have access to the house all day, this can trigger breeding and hormonal behavior. And some pet birds do not stay tame if they remain fully flighted. You have to decide what is more important – having him as a tame pet or letting him run wild. Clipping wings is not harmful as long as the bird has other means of exercising – a large cage, toys, being out and getting handled. With a cockatiel, a wing trim mostly just slows him down anyway. Most clipped cockatiels are still able to fly away if they are outside and catch some wind. So I would suggest having his wings clipped. This will settle him down and help him to remember that he is dependent on you in order to come out of his cage. You also need to establish his dependence on you. Don’t let him come in and out of the cage at will. If he wants out, he needs to be nice and get on your hand and come out. If you allow him to play on top of the cage, close the cage door. That way when he wants a snack, he needs you to put him back in his cage. There is nothing wrong with bribing him to go back in his cage. If he has a favorite treat, only give that to him as a “bedtime or a going inside the cage” treat. And don’t have bedtime as the only time he goes in his cage. He shouldn’t be out if you aren’t in the same room supervising him. If you need to leave the room, he needs to go back in his cage and get a treat for doing so. Once you establish some rules and a routine, he should be a better pet. His feathers will grow back, but if you have been consistent with the training, the bad behavior may not return. If it does, then it is time for another wing trim. It is really the only way because as long as he can fly, he can get away from you whenever he wants to.
Thank you for asking Lafeber,