Kittens are usually considered to be adults when they're around 12 months in age. Although adult cats usually don't sleep as much as kittens, they too can boast pretty impressive shut-eye hours. Normal mature cats that are fit as a fiddle often sleep for between 13 and 18 hours daily. If you ever notice any patterns in any kitten or adult cat's sleeping routine that seem unusual or excessive to you, however, do not hesitate to schedule an appointment with the veterinarian.