Right, some greys are great sound mimics, some become great talkers, some do both and rarely some will be rather quiet. But Greys never stop observing, closely studying their surroundings, their flock , etc, etc. You can try one of those repeating boxes to get him jump started with talking, thats what I did with Salty ( not a grey, but an Amazon specieis that can be good talkers). We started him off with Hello, and a few other words, and once he got the idea that he can talk back to us, whoosh , he started to pick up other words from our daily conversations, and we stopped using the box pretty quickly. Also, some parrots like learning from videos of other parrots talking or singing, from Youtube. Thats where Salty gets most of his talking now, he is partial to listening to Indian Ringnecks and other Amazons. He doesn't react to greys, cockatoos or macaws talking. SO you might try letting him listen and watch some vids of other parrots talking.