Pickles is my 8 year old CAG and we stopped counting the words in his vocabulary a long time ago, at over 150. He talks in entire sentences often, such as "Step up and go get some supper", "Doncha wanna go for a walk to the aviary?" etc.
He will often speak just to hear himself talk but he knows what he wants, can ask for it with his words and constantly amazes us with his cognative abilities. I think a good example would be 'scary'. He never uses this word except when he's been startled, scared or we present him with a new toy that he doesn't like right away.
He never says "Good morning" except in the mornings. He never says "Lights off" unless he wants to go to bed. Things like that.
A really cute one is "There's a bug!" He says this if one flies past him, or if he sees an ant or spider crawling on the floor but one day, while looking out the window, a hummingbird hovered in front of him. "There's a bug!" he hollered. I told him it was a hummingBIRD and he said "Baby butt?" He calls all small birds baby butts.
He'll say "Want some music?" but if you play music he doesn't like, he'll give you the buzzer and say "Want some GOOD music!"
He says "pudding" but he will also say that for jello. In his mind, anything served up on a spoon is pudding. However, if you hand him mashed potato on a spoon, he says "mmmm, potato".
On nice days, we sometimes make drinks and take Pickles outside to the aviary while we sit next to the trout pond. The minute we put ice in our glasses, Pickles perks up with "Juice?" (we don't correct him because otherwise he'll be blabbing to everyone about our drinking!) "Wanna step up and go party in the aviary? Want music!"
We spend a LOT of time with Pickles - we use to take him to work with us every day when we owned our business, and we interact with him constantly. He has play stands in every room and he only goes in his cage to eat or when he decides it's time to go to bed. He is not clipped but prefers not to fly unless startled - and he flies well. Anyone who spends as much time with their bird as we do, knows African Greys aren't just mimicking. We don't 'teach' him words, he learns from normal conversation - either between us and him, or my husband and myself. Sometimes he picks up words that i have no idea where they came from. He doesn't mumble while trying to learn new words, he just spits them out suddenly.