Some cockerels will start crowing as early as 4 weeks. Some hardly ever crow, depending on their breed and their place in the pecking order. The Cochins are usually not really much of crowers, but I am not sure of the BSLs. I would think by they time they reach about 3-4 months you can start hear some of them trying otherwise.
If you are trying to distinguish your boys from girls though, just post their pictures and I am sure people on here can help you figure it out. Get a nice side shot to show legs, combs, wattles and feathering.
Good luck
My cochins crow all the time. The "teenagers" are all up on the fence rails "practicing" in the morning.
It is like high school all over again. Cock-er-doodle-ro-oo-ooo.
my black cochin crowed at around 7-9 weeks
my silver spangle hamburg 7-9 weeks
my black blue andy around 7-9 weeks
these 3 sound so much alike it's hard to tell which one is crowing unless i see them
my golden seabright 9 weeks(heard his first crow this morning)
It really depends on the rooster. I've had some that don't crow until 14-16 weeks, my welsummer rooster began crowing at 4 DAYS old, and I had an Ameraucana chick that started crowing the day after it hatched.
true it depends i have a d'uccle that started crowing 3 days before being a month old..but now rarely does
and a serama that never did till 9 months old now he wont stop