at what age can a rooster start to fertilize eggs?

[Runawaylobster]

I just got fertile eggs from a 4.5 month old blue copper marans roo. I didn't think they would develop but they are!!

 

[BY Chicken Lady]

Following up my previous post about my 13 week old Barred Rock mating with my laying hen. He was fertile...I have a 1 week old baby chick out of their mating. I collected five of my hens eggs that week and cracked four of them finding the fertile Bullseye in all of them. Then I put the fifth one in the incubator and now have a baby chick.

So the answer to the question about what age the cockerel can be fertile...in my case, 13 weeks!

BTW, I have no other roosters and I know the cockerels exact hatch date so there is not age discrepancy. I have two more of their eggs in the incubator now, due to hatch on 8/21. They made such a cute baby I had to hatch some more.

 

[rotagen]

I've got an Isbar roo "mating" constantly with my faverolle hens. He's 5 1/2 mos old now and has been going for it at least a month. I thought I saw bullseyes in some eggs so I went for it about 25 days ago. Candled all the eggs at day 8 and saw nothing looked encouraging. So I cracked one and there was a little well-formed embryo, so I went through the incubation period. Result? Nothing. When I did eggtopsies ...not a single embryo...what are the odds? (14 eggs).
From watching him mate, I would say he's not quite skilled enough yet...like someone said , he's not hitting the target.
Hoping for better luck at 6 mos. and also hoping the bullseyes are easy to spot...my vision ain't great. Isbars are smaller than faverolles but very graceful, he's about the same weight as them, thanks!