It may take him a while to warm up to you, depending on his prior owners. If they provided him with proper care, he will have no reason to distrust you and will probably warm up to you withing a few months. If he had an abusive past life or was neglected, it could take some serious time and dedication on your part. I certainly hope you have large parrot experience before taking in a older re-homed parrot. It is an extremely difficult task. It has been 2 years, and our 11 y/o amazon is just getting to the point where he will let us touch him besides stepping up (he's letting us kiss his head and scratch his neck). He was previously abused/neglected and bounced around from god knows how many houses. I have large parrot experience, a lifetime of it, and I never imagined it being this difficult to take on a bird with special needs.
Then we move on to talking. What exactly makes you think he will ever talk? Some birds do, some don't, and they have the ability to learn new words/sounds at any age (although if they aren't talking before reaching sexual maturity, about 5-6 y/o for large parrots, they probably never will). Encourage his individual talents. Some parrots are extremely intelligent in the ways of solving puzzles (not the cardboard picture kind, they will shred those). Some love dancing (our amazon). Some love talking and mimicking every new word and sound they hear. And if he isn't talking after a year or 2, don't bother teaching him. He'll have his own special talents for you to enjoy. And you never know, a re-homed parrot may have a trick or 2 up his sleeve. Our amazon didn't squawk, whistle, talk or make hardly any sounds whatsoever for the first year we had him. He was the quietest bird ever, the only noise he made was a goose like honk when he was happy. We thought he was essentially mute. About 18 months after we got him, he shocked the hell out of us. We gave him a noodle one night as a treat, and he replied with not his usual honk, but a very clear and enthusiastic birdy "thank you!". He's been talking, in context since, and actually has a very large vocabulary (around 50 words) and can "whistle" along if he hears a tune enough times. We know we didn't teach him, so somewhere in his troubled past, someone spent a very good amount of time teaching him (birds may pick up words, but learning to use them in context is a very difficult thing to teach them). You just never know with a bird. Good luck, and I hope you are up to the challenge.