A female cat is ready to mate when she reaches puberty, which is at about 6 months old. Puberty in female cats is called estrus, which is when she goes into heat and begins her fertility cycles.
Once the first estrus has begun, the cat continues going through a cycle every three to four weeks. During these cycles, the cat is able to mate. Cats that are in heat have a tendency to wander when they are outdoors, as they are looking for a male cat to mate with. A female cat shows signs of her mating stage by sending out loud and high-pitched calls. Cats are also more friendly and affectionate during this time.