How old does a rooster have to be to be able to fertilize eggs?

I have a little baby rooster, and he is about 3 months i believe, maybe younger. He crows and does everything like a full grown rooster would do. He even tries to mate. I need to know if he is old enough to start fertilizing eggs? I mean he mates, or tries, but i don't know if he can fertilize the eggs.Also, hes a frizzle, its a brand new breed of chickens. He crows and mounts the hens, but hes probably about as big as your fist. lol. But i really dont know.

you might have a banty they are smaller than normal chickens,they look like normal sized ones though,but normally they have to be around 6 months,mine is just starting to mate,and learning to crow...EDIT: maybe they don't get very big,and he is mostly full grown? I dont know,you could try to breed them,you really have nothing to lose....if the hens are broody...

Usually, if they're old enough to crow, they're old enough to make chicks. Crowing is an indication that his little man hormones have kicked in and he should be fertile.If he's mounting the hens, he's old enough to breed. Depending on the breed, cockerals can be considered sexually mature by 4-6 months of age. Some breeds mature younger, some older. He's still a young bird, and won't be at his mature size until he's about a year old. But even though he's young, he's old enough to breed some chicks for you.