I had two bantam rooster that started to crow between 8 and 9 weeks. My meat birds roosters will sometimes start to crow right before they are processed at 8 weeks.
I would say yours is overdue in the crowing department.
12 weeks is right on target, depending on whether he has competition, my silky boys are 3 mth old and have just started to crow having a few days break in between.
Im sure he will fire up, he is just practising and possibly embarrased!
My buff rock and buff orpington roosters both started crowing on the same day at 15 1/2 weeks old. My barred rock rooster I adopted hasn't crowed yet and he is about 22 weeks old.