My Hahns Macaw is still being hand fed and enjoys neck scratches both in and away from her cage. She will not step up onto my hand from her cage though. I have to offer her my forearm or shoulder.
My Velcro adult Sun Conure couldn't get close enough to me - but hands were a no no. If I wanted to scratch his head, I could do so with my chin, nose or any part of my face - but fingers were not allowed. It was almost like he didn't recognise that my hands were part of me. For a very long time (years) he lunged at them when he saw them. At the time he could be sitting on me, snuggling into the crook of my neck, but at the same time my hands were the enemy. He never ever bit though.
This did improve, but hand were never accepted. Also, even though he was re-homed to me at 5 years, I'm confident that I know his history and he was never abused and was a well loved hand raised bird. He just didn't care for hands and sometimes you just have to accept that about your bird.
So my advice is offer your forearm, with a treat as a reward when he steps up.