It varies from breed to breed and individual to individual. But generally once they can make contact, they can fertilize eggs. Not just go through the motions, but make actual cloacal contact. At 6 months fertility seems to increase. Is it a factor of age or ability? I'm guessing ability since lighter, more agile, less fluffy appear to show fertility earlier than larger, clumsy, "over fluffed" breeds.
My Barred Rock cockerel has been chasing all the girls around the last few days. Only my laying hen will squat for him...so far. I watched him appear to get the gymnastics down pretty well, then he jumped off and she stood up and fluffed her feathers then checked her own bottom. Do you think he is already fertile and completing the task? He is only 13 weeks old.
I wouldn't think your BR could be fertile already but what do I know. I've got a question since we're talking about when he becomes ready to fertilize eggs, at what age do they lose their fertility?