A cat's age can be determined by examining it for signs of sexual maturity and by looking at its teeth, coat and eyes. The presence of baby teeth and the amount of staining on the teeth are clues to age. Several behaviors and physical characteristics are indicative of sexual maturity, which occurs at approximately five months. Fur and eye changes can be used as general indicators of approximate age.
Kittens have baby teeth that emerge in their first two to four weeks of life. These teeth are replaced by permanent teeth by the time they are three to four months of age. The older a cat, the more stains it is likely to have on its teeth. These stains result from the build up of tartar, which increases with age. If a cat's owner has diligently provided dental care, tartar build-up may not be a good indicator of age.
Male cats mark their territory by spraying and develop more prominent testicles when they reach sexual maturity. Females first come into heat during this time. They become very vocal, using a distinctive howl when they are in heat.
Kittens have fine, soft, fine fur that becomes coarser and thicker with age. Older cats may have patches of gray or white in their fur. A kitten's eyes are also clearer than that of an older cat, with no tearing or discharge.