Both roosters and hens vary in when they show their "signs of maturity". Some hens start laying at 16 weeks while others wait for over 30! Same with roosters. I had one that started at a week of age and some wait until they are fully mature to give it a try.
I would guess a hen should begin...
My sebright mix boy, Lil' Dude, showed off his sebright spirit and started crowing at 1-week!! He was still in the brooder and not even feathered and he hopped up on the side of the brooder and attempted a crow. Silly boy.