Yes, the answers can be all over the board. I've had both cream legbars and old English game bantams crow at three weeks. Actually it sounded like they were being strangulated. Now I have three 3 month old Old English game bantams and they have their crows down pretty well. They sound like small echoes of the large rooster. My oldest rooster was over 7 months. If there are other roosters in the flock it might encourage them to crow or a more submissive rooster might not crow under those circumstances.
If I had to chooses an average it might be 4 months, but some are sooner and some are later.