My first rooster crowed for the first time at 17 weeks. We live in the city where roosters are not allowed, so he had never heard another crowing, even in the distance, and I would have to say, his first attempts did not sound at all like a rooster - hey, he had nothing to go by. My theory is that if they live in an environment where they hear other roosters crowing, they are more likely to crow early but I have no data to back this up. (Incidentally, he was one of four roosters from a straight run. Since his crow didn't sound like a rooster, I let him stay on for a couple of weeks after that but finally decided it was time to process him and did two of the others while I was at it, even though none of the others had ever crowed. I decided to let one live on, thinking we might have a few weeks before he started up. Turns out, as soon as the dominant roo was gone, he was ready to strut his stuff. He started crowing the day after I processed the first three - and he DID sound like a rooster. Within a week he was crowing loudly all day, every day and I had to process him before the neighbors started complaining).