When should i get my male cat neutered? he is 5 months?

A cat can be neutered as early as 8 weeks of its age although it is usually done at 4 - 6 months old. Undesirable behaviour patterns may be more difficult to alter if cats are neutered when they are older. It is now becoming increasingly common for cats to be neutered at an earlier age (2-3 months old).
So, you should get your cat fixed as soon as possible, now would be the right age to get him neutered .