Is there a chance that he will get a full vocabulary, since he is an older bird and just now beginning?

Remember that hand-fed babies are a relatively new innovation. It wasn't that many years ago that most of the parrots in the pet trade were wild-caught, imported birds, and many of them were adults. Yet, Quakers *developed* their reputation for being good talkers under these circumstances.

Adult birds do not stop learning, and are quite capable of learning new things at even advanced ages, just like people. Whether your bird learns to "talk" will depend on how much it wants to communicate with you and imitate you, so if you work with your bird a lot and develop a strong bond of love and caring, it is very probable that your Quaker will begin trying to communicate with you in YOUR language.