It all depends on the rooster itself and if there are other roosters around. Average without other roosters is about 3 months. I have had some take 9 months with other roosters around whereas there are videos of 2 day olds crowing in the brooder after hearing another one crow. Keep in mind that while rarer some hens do crow as well.
I had a 9 week old true ameraucana crow yesterday, well, it's attempt at a crow, I have several others between 9 and 10 weeks old and not even an attempt yet from any of them...they're all still peeping...lol..foreverlearning is right, all depends on the rooster itself...