If you are not planning on breeding from your cat and intend on allowing them access outside, neutering at a relatively early age can be beneficial both behaviourally and for physical health throughout their life.
Castration for male cats.
Spaying for female cats.
Castration and Spaying at 5-6 months of age.
This is especially important if you have both male and female kittens or your female cat is going outside before she is spayed as she will get pregnant before you realise. Your vet will be happy to explain in more detail and make recommendations for your individual pet.