Teeth
A cat's first baby teeth erupt in 2 to 4 weeks, so looking at the teeth is a good way to determine a kitten's age. Their permanent teeth develop on top of the deciduous teeth, and by the time kittens are 3 to 4 months old, the permanent teeth will begin to replace the deciduous teeth. Typically, all adult teeth are in place by 6 months of age, and teeth can no longer be used to determine age.
For older cats, the amount of stain or tartar on a cat's teeth is also an indicator of age. However, pet tooth cleaning products can be found everywhere , so tartar may not be easy to judge, mainly depends on whether the shovel officer has done good dental care for the cat. So while teeth can be used as a measure of the approximate age of a cat or kitten, it is not foolproof.
Sexual Maturity
Male cats are sexually mature as early as 6 months, and signs of estrus include territorial marking behavior and a more pronounced egg. Female cats generally start their first estrus between 5 and 8 months. After entering estrus, it will be very obvious with the voice, but the length of sunlight and the cat's weight can also affect this. Female cats are most fertile between 18 months and 8 years of age, and can become pregnant at other times depending on the circumstances. However, many veterinarians now perform early neutering of cats to help prevent early pregnancy, which is more difficult for both mother cats and kittens, and the surgery itself is said to be easier for younger cats. So using estrus to determine age can be a little tricky.
Hair Growth
A kitten's coat is fine and soft like a baby's, but it thickens and thickens as the cat ages, and may become darker or lighter in color. As cats age, they can even grow white or gray fur, just like humans do when they age. Hair isn't necessarily absolute evidence of age, but it helps determine a cat's age. In addition, cat licking can also help determine age. Cats are very clean animals, but older cats may start to lick their fur less often when they gain weight with age, or when they experience dental problems or pain from arthritis.
Eye
The eyes of healthy kittens and cats on dry maintenance are very clear and bright, with no signs of tearing or discharge. Older cats, however, may have cloudy eyes and start watering or discharge, which generally doesn't occur until at least 10 years of age.
