There are lots of different opinions about this. Some reputable breeders support early speutering, and some say to definitely wait until 6 months. I think I'd go middle of the road and get them done at 4 months as long as they are a healthy weight. It's a lot easier on a male kitty than a female, so I wouldn't worry about it as much with him. As for your girl kitty, just make sure she doesn't get out again if you wait. Call your vet and ask what they recommend.