My little 5 week old Gold Sebright is already squeaking out a few crows a day. I wonder if bantams mature faster. The standard roos I have had took their sweet time deciding to crow, not a sound from them til 4-5 months.
I have 3 roos out there right now (in my suburb!) and I keep waiting for crowing. My Polish is 14 weeks or so, only crowed quietly once 3x in a row a few weeks ago and never again. The 14 week old EE roo has never crowed. And the 18 week old Brahma once made a loud odd squawk but has never showed any other signs of crowing.
I think with the breeds listed in your signature experienced people on BYC can probably tell, if not make a very good guess. I could tell my BO's were roos by 5 weeks, and my two EE roos were looking suspicious at that point too.