How old should a male kitten be before he is neutered?

Our male cat had the op at 6 months old.

According to KittenCare.com, "You can have [male cats] neutered anytime after 7 weeks, although 4-6 months is the norm." So, at 5 months, your kitten is right on the mark.

I usually like to wait til they are about 6 months of age til maybe 9-10 months.. Most males I have had are acting MALE at 11 months, but 9 is also possible. I don't like to fix them to early as I believe they need to get some of those male hormones in them. I had a cat when I was young, (So my mother was in charge) We fixed him at 4 months old. Let me tell you he looked ODD. His head never got to mature (as males heads tend to get bigger) so he had this tiny little head. and this huge 18lb (yes that was his NORMAL AVERAGE Weight) body But skinny little legs. His rib cage was quite wide so he probably would have been a Tall yet big cat- but because he never had those male hormones working his body never quite new what to do - so he looked weird and always tended to be heavy. I truly believe if we had waited at least 2 months he would have looked like a completely different animal.