My vet told me that male cats need to be 6 mo old cause they need the hormones for their urinary tract to develope properly or they will probably have urinary problems when they are grown. I know that they now nuter both male and female at a very young age now because of over population but if you do it properly, 6 months. Females, after their first heat. Treating urinary infections in your male cats can get very expensive and if they are indoor/outdoor cats they are very hard to medicate cause they are never around when it is time for their next dose. Ask me how I know.