It is not likely that he will stop this behavior once it has began unfortunately, aside from the usual reason for getting your male cat fixed at a young age of 5-6 months to prevent overpopulation this is another reason that it could have been prevented before now.

Once a male cat starts this it will not stop! It is a natural hormonal issue.

 I can't tell you for sure that neutering your cat now will completely stop your cat from spraying, but one thing is for sure, if you DON'T get him fixed, he will continue to spray. He's marking his territory.