Depends on the roo. I've heard some start at 7 weeks, I have one now who is 20 weeks and still hasn't crowed or made any attempt at all...some have gone as long as 30 weeks before they start.
Ike waited for his 20th week birthday. So far he's not being obnoxious about it (a minute or so burst a couple of times a day), but I keep reminding him that we have neighbors, and I have no need for fertilized eggs.