There are a lot of mysteries about cats that have been adopted or rescued, and that includes the feline's age. A veterinarian is your best partner in determining the current age of a cat, as well as in planning a care program to ensure the optimal quality of life and longevity. A thorough veterinary examination of the cat's entire body will generally help to determine an approximate age of the cat; however, vets tend to look at a few body parts in particular when trying to estimate how old the cat might be.
Teeth
A cat's initial baby teeth first emerge between 2 to 4 weeks, making teeth an excellent determination of age for kittens. Their permanent teeth are developing above the baby teeth and by the time the kitten is 3 to 4 months old, the permanent teeth will start to displace the baby teeth (also called deciduous teeth). Typically, all of the adult teeth are in place by 6 months of age, and the growth is no longer useful in determining a cat's age.
In older cats, the amount of staining, or tartar, on a cat's teeth is also an indicator of age. However, with pets' teeth cleaning products readily available, tartar may not be a good indicator depending on the diligence of the cat's caregiver in providing a dental care program. Therefore, while teeth are a good indicator of a cat or kitten's approximate age, they are not foolproof.
Sexual Maturity
Male cats reach sexual maturity around 5 months. Signs of puberty include territorial spraying of urine testicles that are more prominent.
Female cats will have their first heat (estrus cycle) sometime between the ages of 5 and 12 months, though the length of daylight and weight of the cat also have some effect on the time of the queen's first estrus cycle. A female cat will tell you she is experiencing estrus very visibly and vocally. A female cat can become impregnated and give birth to her first litter by the time she is 7 1/2 months old.
However, many veterinarians now practice early spay and neuter. It not only helps prevent early pregnancies, which are harder both on the mothers and on the kittens, but the surgery itself is said to be easier on the cats at a younger age. This can make determining the age of a cat a bit trickier.
Coat Development
A kitten's fur or hair is baby-fine and soft, but as a cat ages, its coat will thicken and coarsen. It may also change color, becoming darker or lighter in shade. When a cat attains senior status, it may even develop patches of white or gray individual hairs, much as humans do upon aging. While it's not a guarantee of age, the coat helps a vet determine the age of a cat.
Additionally, how well a cat grooms itself can help indicate how old the animal is. Cats are incredibly clean creatures, but an older cat might begin to slack on grooming as it gains weight with age or when dental problems or arthritis make it painful.
Eyes
Healthy kittens and cats during their maintenance years have eyes that are very clear and bright, with no evidence of tearing or discharging. Cats in their later years, though, may develop a cloudy appearance of their eyes, including tearing and/or discharge. This doesn't usually happen until the cat is at least 10 years old.