When you come across a stray cat, it can be difficult to tell its age, especially if it already has its adult teeth. Kittens receive their incisors at 2 to 4 weeks old. Their canines come in when they are 3 to 4 weeks old, and their premolars come in when they are 4 to 6 weeks old. By 8 weeks, kittens should have all of their baby teeth. When the cat is 6 months old, all of its adult teeth will have replaced its baby teeth. It becomes challenging to accurately determine a cat's age after it has all of its permanent teeth; however, there are some characteristics to look for that can help estimate a cat's age.
Examine the cat's teeth to determine if it has its baby teeth or adult teeth. If it has its permanent teeth and they are white, the cat is at least 16 weeks of age. If its back teeth have yellowish stains (tartar), the cat might be 1 to 2 years old. If all of the teeth have tartar buildup, the cat might be 3 to 5 years old. More wear on the teeth are usually seen at 5 to 10 years old. By 10 to 15 years, the cat might be missing some teeth and have an extreme amount of tartar buildup.
Look at a cat's eyes to see if there is any cloudiness in the lens. Like people, cats can develop cataracts. A cat with cloudy eyes might be 12 years old or older. Also the iris of their eye is smooth when they are kittens, but as they get older, it becomes more jagged and crackly looking.
Feel its body to see how muscular or bony the cat is. Young cats are more likely to be in shape and be toned. Older cats might have extra skin hanging, and their shoulder blades might protrude more.
Monitor their habits. It's not always the case, but cats are usually more playful when they are younger. Older cats prefer to sleep more and are not impressed by toys.