I have a 14 year old Grey that I enherited from my Sister about two years ago. At the time that I adopted her she had never been to an avian vet, I promptly took her to one and he told me to switch her from seed diet (which was all she had ever been on) to Harrisons high potency pellets. He said that the pellets are a complete diet, however I do supplement with veggies, fruits and some nuts and seeds in moderation. Because Greys are prone to calcium deficiencies,the high potency pellets are a good fit. I also take Rose yearly to her avian vet for blood work which is very important (which I would have never known) to make sure everything is ok with her.
Good luck, I hope maybe this will help you.