Do you have any other roosters that do crow within hearing distance? Usually cockerels don't need an example to start crowing, but I had one that did. A long time ago I rescued a cockerel from the middle of the highway that fell off a poultry transport truck when a door unlatched. His cage mates did not survive, but Frank became a pet. I did not know it at the time, but he was a "meat bird" raised in a small cage. He had to learn how to walk and drink from a bowl, but he was docile and very friendly... and he did not crow. Another point in his favor. 
I warned the man who shared the small property where I lived... Do NOT CROW at Frank. I didn't even want that bird to know what crowing was. Well, months later this man had a friend over and he took the friend out to the barn to meet Frank, and guess what.... they crowed at my bird! And guess what... Frank immediately crowed back. A lot. And loudly. 
I was not happy. I suppose Frank would have eventually crowed one day, but having an example certainly sped up the process. Genetics? Probably.
