It's rare, but it happens !
Some mate and don't lay, other lay but I never saw brooding at this age!
It happens when they are from very early in the year, weight plays a role too!
I agree with Dany, very early hens can lay between 12 and 16 months of age but not often and less often are they fertile. I have a Feburary hatch IB hen split Opal SP, so it will be interesting for me to see if she lays next season.
Based on my observations, Ive heard of true yearlings laying eggs but never had one myself. Usually its a very early spring hatch hen that might lay as a yearling but as stated earlier they are most likely above 12 months old . With a good mature rooster an IB hen will usually lay at 2yrs of age. They are normally not regular, meaning they dont lay every other day and will lay 1 day and wait 2 or 3 days until the next and they are notorious for perch bombs, but will lay. I have heard of 1 yr old roosters mating but would attribute the vast majority as early hatch birds. The roosters reproductive organs usually are not developed enough at a year. A 2 yr old IB rooster can mate and are usually fertile but, from my experience they dont have the mechanics down and need practice. At 3 years of age, there is no excuse for infertility in an IB rooster. FYI the above does not fully apply to green peafowl. The hens might lay at 2yrs old and if your depending on a 2yr old green rooster to mate and be fertile you are probably going to be disappointed. 2 yr old green roosters are normally not ready, at 3yrs and above there is no excuse for infertility. I hope I helped,
I have a 15 month old peahen who laid 4 eggs and now is broody. Her mate is a healthy 2yr old.. Ive seen them mount, so we will see soon if her eggs are fertile!!