Wow! 3 months old is very young to be spraying already, so I assume that the others, like me, are pretty stumped by this question?
Is he actually spraying territorially (have you seen him?) or is he just urinating in inappropriate places? It might be worth getting a urine sample down the vets to rule out infection.
If it is territorial making, and he hasn't been doing it for long, neutering will probably stop it. Although he is very young, as long as he has visible testicles they can be removed!!!!
Good luck, Ems x