Get your cat neutered or spayed unless you plan to breed it and breeding should be left to those who are very serious about it.
Benefits of altering include improved behavior and suitability as housepets, no unwanted kittens, reduced motive to get outside or damage the house and a marked decrease in many medical problems, including mammary cancers and uterine infections. The ideal age for altering is 5 to 6 months, before most sexual behaviors develop and before females experience their first heat.
Neutering or spaying includes a small surgical risk, inability to breed the cat later and a tendency for the cat to gain weight (easily controlled by dietary management). Altering will not stunt your cat's growth, and studies fail to link early altering to later medical problems.