I am not sure how much help this will be but I will try to give you some insight based on my experience owning a CAG so far. I did an insane amount of time putting in the hours researching and reading about CAGs before I went and looked at the CAG I now own. I have a 5 y.o. CAG who will be 6 this spring that I bought from a man last July (so roughly 7 months ago). Her previous owner had been her only owner up until me and was the one to wean her (to give you an idea of how young she was when he purchased her). They had an incredible bond and she was very attached to him but had been very well socialized. She adjusted immediately when I brought her home and had no problem letting anyone hold her. She has become extremely attached to both my sister and boyfriend (to the point where she regurgitates for them). So while a lot of sources will say that a CAG will tend to be a one-person bird, not all will fall into that category, as I own one who is the exact opposite and can be handled by anyone without problem. Based on this, I would think that it is extremely possible for you to still work with her and that you two can create a bond as long as you are willing to put in the time and effort. I was lucky enough that my CAG has an easy-going personality and made the bonding process almost effortless. The fact that you can pet her on occasion is already a step in the right direction. CAGs aren't cuddlers or overly affectionate birds in general. Mine isn't a big cuddler but loves a good scratch every now and then.
As far as learning to be out and social, that can also be accomplished with time and working with her. My CAGs previous owner would take her out in public to the beach or wherever else as a way to socialize her. When I brought her home I would introduce her to new people whenever company would come over.
African Greys in general are known for their dander and are one of the dustiest, if not the dustiest, birds. She gets a bath at least once a week to help keep the dust down and help keep her skin from getting dry.
Being 21, I am not sure if she can learn more words and phrases. I know the AG, Einstein, was learning new things all of the time and he was in his 30's, so I suppose it is possible.
As far as what you can do to enrich her life and not be locked up in a cage, just really put in the time with her to help create that bond. Making sure she gets several hours out of the cage each day will help reduce screaming and plucking behaviors. Keeping a lot of things available for her to do when she is in the cage is a must (toys, foraging wheels, etc). Keeping her somewhere where you spend a lot of your time so she can feel like part of the 'flock' will help her as well. I have my CAG in the dining room (it is an open concept so it moves right into my living room so she can see the living room, dining room, and kitchen) so she can always see where we are at and be engaged in what we are doing. I play the radio for her when I am not home and she now whistles part of some song.
