We really did think Big Kitty was a female when he stayed in the house for his first Christmas! He moved out shortly thereafter.
Telling the girl cats from the boy cats when they're little is difficult, but it really doesn't matter when they live outside. The males can mark their territory and the females can have a litter of kittens. We introduce new bloodlines, and if necessary, give away females sired by the dominant tom. If there are too many toms, they find a new home or Dr. T sharpens her knife.