They'll still learn to talk, just maybe not learn a huge vocabulary.
Sisqo is 10, and has always said "hello", "sisqo", "sisqo bird", "hi", "pretty bird", "bye", "ma" & "mom".
Latey though, he's been muttering "step up", and "what's up".
So yes, you can still teach them to talk, but make sure you give them a lot of praise, even when you hear them just attempting it. You can tell when they're kind of struggling with it, because they'll mumble and grumble it to themselves until they get it just right, and then it'll come out clear as a bell.