We are a proud owner of a 'second-hand' slightly used cockatoo. In 2012 we bought him very cheap from a bird store because he had behavior problems. He was plucking his feathers, bites people, and gets scared and starts shaking when anybody approaches him. He bonded with my wife immediately but it took him about six months to bond with me. The bite scars on my hands are proof of his initial mistrust. And then he 'adopted' us.
According to his bracelet, he was born in 1997. After 4 years, he seemed very friendly now but occasionally plucks his feathers when he gets bored. We provide him with wood to chew on and toys for him to play; these distracts him from plucking. It was a lot of work and patience to rehab the bird. But it was also fun and worth it. He acts like a 3-5 year old child.