There is no absolute rule on when to fix an cat or dog. Some vets are doing it right away, others wait until they are a little older. I prefer waiting. Your vet will let you know their preference. We also have a cat that was a stray. It was the middle of winter with extremely low temps. One day she felt comfortable enough to just walk right in with our pug and cocker. She's been with us ever since (about 5 years now). When we wanted to take her to the vet we had to drop her into a pillow case because she was afraid of the carrier. I sure had battle wounds from trying! Now she is the perfect loving pet. Sucker is written over our door.