So the bird may not be retarded, just reacting to abusive treatment by his breeder. That makes more sense to me, given the behaviors that you have described. The problem is that while he will probably improve over time with your gentle and understanding care, he may never get over it completely as the things done to them at that early of an age can cause them problems for the rest of their lives, just like with human babies.
I think that he is terrified that you are going to do the same things to him as his breeder did as biting is usually a last resort for parrots when nothing else works. I would suggest that for now you do not attempt to handle him or ask anything of him. I would limit my interactions with him to just talking and singing to him and giving him lots of "Good bird, his name'" type of praise. I would still offer him a treat, but not expect him to take it, so when he does not take it place it in his food dish and go away for a little while to give him a chance to eat it.
This is an attempt at winning his trust by showing him that you are listening to him ( his growls, saying don't touch me ) as well as to his telling you that he is terrified ( his crying ) by respecting him and not trying to handle him and that you are the bringer of good things ( the treat ) and by leaving so that he can eat it. In time he may begin to growl and cry less and perhaps quit these things. The next sign of progress would be his beginning to look forward to you visiting with him. This is going to take a lot of time and patience as he needs to see that you are his friend and that you are not going to force him so that he can begin to heal from what was done to him.
This is why I have the birds that I do. They were all abused and mistreated before coming to live with me. It takes a lot of time and effort to get some of them to the point that they can begin to heal.





