How Can You Tell How Old Your Cat Is?

Basically cat teeth are counted to measure its age. You can also measure cat's age by comparing it with human age. There is some specific formula that you can use to calculate age of your cat. Your cat age can be measure by growth of its body also.
If your cat is 1 year old that is equal to 15 human years.
In the consecutive 2nd year of cat's age you can add 9 years of human age.
Similarly, in 3rd consecutive year, add 4 human years in your cat's age.

There are many age calculators that are available built by experts so you can use them to find your cat's age.

The best way is to ask your vet

Count the rings in his/her trunk, or hire a cat whisperer.  Sorry.  I couldn't resist.