How early can a rooster do his thing?

I have a rooster who was hatched May 1st and he is just now trying to get frisky with the girls. The crowing seems to precede the mating activity by several weeks to several months. It would be very doubtful that the eggs are fertile at this point, especially since you haven't seen any breeding activity. Have you checked for fertility by cracking the egg and looking for the larger than expected blastoderm on the yolk?

Here are pictures to guide you:

https://www.backyardchickens.com/t/16008/how-to-tell-a-fertile-vs-infertile-egg-pictures

 

Our first pullet started laying when our oldest rooster was 13 weeks. He had started crowing at 9 weeks, and was mating the girls by 12 weeks. I cracked our first 8 eggs open at the same time, they had been laid while the rooster was 13-14 weeks. Out of those, about half looked to be fertile. But if your roo isn't mating his girls yet, then they won't be fertile, but if he is, check the eggs for the bulls eye.

 

I'd doubt your eggs are fertile, but I'm one who never lets a broody go to waste . I think it's a great time of year to let her hatch eggs. Were I you, I'd get on my state thread here, or my local CL, and look for some fertile eggs to pop under her. Local folks will usually sell their backyard eggs for a small amount for a broody hen. I've sold eggs for that, and I've also given eggs on the agreement I'll get half the hatch back when they're weaned. Just cause your roosters aren't ready doesn't mean you can't get babies . Just remember, though, when you hatch, in theory half will be cockerels, and you'll need to have a plan to manage them.