Gentleman bits! How polite!
I have two male Maine Coons. One of them came to me as a four month old kitten and he had been neutered by his breeder at 13 weeks. She had all the kittens which were to be sold as pets, neutered at this age to prevent her line from being bred indescriminately. Also early neutering is supposed to make the cat grow bigger and as Maine Coons are big cats, it is meant to help with that although I don't know how true that bit is.
I tried to get my vet to neuter the other early and he finally agreed at about 17 weeks. I think he was worried that if he didn't do it, I'd find another vet who would.
Why don't you see if your vet will neuter him now. It will save all that worry that he might start spraying soon.