[Sprecker]

I am having a similar adventure with my Too. Same age (20), situation (death of the original owner and I addopted her about a month ago) and attitude (friendly as all get out but won't step up). She even lets me pet under her wings, something my grey wouldn't let me do without a screech.
From what I have learned from the month I have had her was that if you keep constant attention giving and offer a treat every time you spend time with him/her. Nothing you probably haven't been doing already. Eventually s/he will just want to be around you. Then stepping up.
Amber (my Too) still refuses to step-up yet and only lowers her head for scratches. She will fly over to my shoulder or back of my arm chair if I am in the room and not giving her enough attention. The odd time she will step on to my arm but never on command. This makes bed time an adventure that goes on for way longeer than it should.
I know that these are totally different types of fids and have very different behaviours in general but I believe the principle is the same. Trust.
I wish you good luck and all the best.