I have normal greys, whiteface, pearl pieds, creamface cinnamons, and pearls.
You've already done a wonderful and loving thing by taking this grumpy old man in! At his age, about all you can do is make him as comfortable and loved as possible. Keep in mind that due to his previous owners age, Joey probably didn't get much attention and was pretty much left on his own. I would for sure get him a better cage filled with toys and perches. Now as to the diet, that may be a tuff one. I would TRY him on a good blend of tiel food such as Rowdybush and see how he takes to veggies such as broccoli. DON'T expect drastic changes over night. it may take him a while to warm up to not only his new home but what he eats as well. Do you have any photos of him?