My old boy was neutered at a very young age (I adoped him and use the same vets so they have his full history). I did have an entire male that was about 3 before he was neutered, he never strayed, never sprayed and when he went in his tray even his pee didn't smell - dunno why, I got him done when he had an accident with his back leg and had to have his leg set in plaster, the vet 'did' him for free! My female cat was in season when she was spayed (both my other cats were seen to so she was safe). All of my cats have been neutered, my latest cat (we've had him for 6 or so years now) was rescued, he stank of tom spray, he was confined until he was well enough for his operation (RSPCA and the CPL paid for him to have tests as he'd had a unfixed broken pelvis, and his neutering as well as blood tests for the usual as he was a stray that I'd taken in as he was so poorly). If you aren't going to breed from them then you should neuter them theres enough unwanted kittens in the rescue centres as it is.