Cockerels (roosters less than 1 year old) usually start crowing before they start trying to go after and tread hens, so you guy may still be growing. Also, adult roos tend not to really "see" very immature females, so it's possible your non-breeding cockerel, as he grows into roosterhood & realizes what he's supposed to be doing, looks around and sees only an immature female - this could be the cause of the delay. If he has access to other, older females, see how he acts around them. It may be you just have a wait a little while longer.
And it's not always obvious that mating is occurring when it is. Many a poultry-keeper (myself included) incubated chicks or left them under a broody hen only to find a few that were obviously from the lesser of 2 roosters, one never caught in the act of mating anything, or even trying. My gorgeous black Langshan ruled the roost and barely tolerated the ugly little silkie roo. The Polish hens (bottom of the pecking order) had laid eggs that I put under a mean turkey hen to set. I was sure those eggs were infertile b/c the Langshan and the silkie roos ignored the Polish hens completely. Was I wrong!! Three of the ugliest Polish-Silkie cross chicks hatched, their silkie heritage unmistakable - black skin, 5 toes, feathered feet. My silkie roo was just a sneaky mater!!
So, signs of healthy roo mating behaviors / sneaky mating: Roos will begin doing some chicken mating behaviors while they are still cockerels, usually starting around 6 months of age. Toss them some food, or a treat, and see if they call the female chickens over. This act, called the "food call" also called "tidbitting" usually involves the roo picking up & throwing down & picking up pieces of food, while calling with a soft something like "buk-BOOK-buh-BOOK-BOOK", and the females come running to eat the food. Of course, now he's surrounded by females and can start a mating dance (or just grab one of them by the back of the head & climb on - some roos don't dance), which involved dropping a wing and hopping in a semi-circle around the female of his choice. She usually responds by squatting (which hens sometimes do to their keepers as well - a lowering of the body & tucking of wings that looks like nothing else). Then he grabs her by the back of the head and climbs on.
If your older roo is food-calling/tidbitting, and your hens have bald patches on the back of their heads, or broken feathers on their backs (from his feet) then you probably just have a sneaky mater, like I do. Another way to find out is to incubate your eggs & see what grows. If you're not sure if you've seen these the mating behaviors, you can probably find videos on youtube I bet. Just be careful what you type in for your search!!
