Male cats will start to go into heat around 8 months old, and female cats will start to go into heat earlier than male cats. Some female cats will start to go into heat for the first time when they are 4 months old. The specific time of heat depends on the cat itself. Circumstances dictate. Cats come into estrus relatively early, but they have to wait until they are over one year old to mature before they can mate. Female cats have an estrus cycle every 20 to 28 days, lasting 3 to 7 days each time, while male cats have no fixed estrus cycle.