This is crazy to me because my cockerel didn't start to attempt to mate until 5.5 months old. He didn't crow until after 6 months! He was the only boy so maybe that's why? No competition so he could take his time.It varies of course, individual to individual and I'm dealing with multiple boys. But average for me noticing around 10-12 wks I see them start getting Randy to the pullets.
But, all of mine grow out in Kongs coop so they have him to contend with and he doesn't allow them to mate in his presence. By 13-15 weeks tho, it really ramps up and I need to separate them out as Kong can't keep them in line especially out free ranging.
Even with multiple boys, all may not be trying, but I go by the first one I spot harassing and they all get moved together.
Having just a single cockerel to take over and be flock master creates another issue as I want him to be schooled by the older hens but if there's pullets present he goes after them and I'll watch to see if the older hens are protecting the youngest by blocking for them or not. In cases like this, if I feel there's too much going on I will separate him out during peak mate times to settle it down. Only allowing him out to free range under supervision.