At how many months is a cat considered one year old?

A cat is considered one year old at 12 months, roughly equal to a human teen of 15-18. Cats become sexually mature around 6-8 months and have their first heat, but their bodies aren't fully developed so they shouldn't breed yet. After one year, the second heat arrives and breeding is possible; if you don't plan to breed, spaying avoids heat-season howling, spraying and mood swings.