The simple answer seems to be when they get ready to. I had one start at 10 weeks, the other not until 15 weeks. I've read on here anywhere from 2 weeks old to more than six months old.
my BR cockerl just crowed again this morning 6:30am Wreid sound, not crowing just cooing with a sqwak. first time was a week ago, for two tries then nothing. this time he tried from 6:30am til 7am and nothing for the rest of the day.