A vet would be able to make a more accurate estimate about a cats age (but still may be a couple of years out in an older cat). They will look at the condition of the cats, teeth, sexual maturity, fur colour and thickness, and the cats eyes. Here's one article that explains the above.
cats.about.com
(can't' find anything about a cats whiskers telling the age of a cat. Larger and heavier cats will often have longer whiskers than a smaller, skinny kitty.)
cats.about.com
(can't' find anything about a cats whiskers telling the age of a cat. Larger and heavier cats will often have longer whiskers than a smaller, skinny kitty.)
