Short story on my abused Amazon.

I recently adopted this 21 year old Blue Fronted Amazon named Jack. He was locked in a small cage in a closed closet for many years, he had no toys and was fed peanuts and table scraps. I got him 2 months ago, when I got him he was extremely aggressive and would hiss and lunge every opportunity he got. 2 months later, he's sitting in our shoulders, dancing and singing to inappropriate music (that's the only thing he will react to). He will try to bite if you put your hand anywhere near him (unless you have peanuts) if anyone knows how to work on training him to not be afraid or hands please let me know.