Neutering is recommended before 1 year of age usually, most people get it done around 5-7months of age.
Dogs don't come in "heat", only bitches do. So he'd be peeing/marking territory constantly. When dogs become sexually mature their pee starts to smell REALLY bad.
You can buy belly bands, which will solve this problem. It's just no fun changing pads full of pee all day, but if you want to use him for breeding I think that's what you have to do!