At what age is a cat fully grown (adult)?

A cat is considered an adult at 1 year old. Because a cat’s lifespan is only about 12–18 years, at 12 months it is already equivalent to a human of 15–18 years.

Cats over 1 year can begin breeding. If you have no breeding plans, you can have the cat spayed or neutered at a vet to avoid prolonged heat cycles that lead to false pregnancy and reproductive disease. After age 8 a cat is a senior; reduce jumping and climbing to limit bone wear.