I have three kitties: Luke (male, fixed, 8 months), Leia (female, fixed, 7 months), and Baby (female, 6 months). While trying to breed Baby, we brought in a male for her (Mr. Peanut). I thought it would be an all-out war between Mr. Peanut and Luke, but it was entirely the opposite! Luke was laying down and barely raised his head as Peanut sniffed him. Leia, on the other hand, was stalking Peanut, pouncing him, and never took her eyes off of him. There were no fights, to everyone's amazement (breeding didn't take place either, even though we left Peanut and Baby alone without the others on the back porch overnight).
I always thought males were aggressive with other males. Could it be that since Luke is fixed, he doesn't feel the need to be aggressive? What about Leia? Why would she be so territorial?
I adopted them all at early ages. Luke was rescued from a shelter at 2 months of age (when I adopted him). Leia and Baby were from the same mother, one litter apart (Leia was 2 months, Baby was 1 month when I got them).