My roos were trying very hard at 10 weeks old. I think one of them finally accomlished it at around 15 weeks old. Whether he was actually fertile or not I dunno, but he sure acted like he'd just won the lottery.
Generally speaking a stag is thought to be fertile when his full sisters begin to lay. Actually, it might be earlier or later though by as much as a couple of months. saladin
My hens started laying at 5 months old.....well some did. The roosters were 5 weeks younger than them, but they were paying attention to the pullets that had the red combs and it looked about right.