We used to breed Wyandottes and will do again soon. By 8 weeks they had all sexed obviously, in that the cockerels had noticeably larger combs and stood more upright. At 8 weeks we had one crow, then stop at 10 weeks because his sibling was dominant. Just for your interest our record for youngest crower is a Leghorn bantam at 3 and a half weeks, prompted no doubt by his older sibling who started at 4 weeks.