So How Old Are You, Anyway?
If you’ve adopted a cat and aren’t sure of her age, here are some things to check to get a general sense of how old a cat is:
The Teeth: Teeth are a great indicator of age. Older cats tend to have more staining than younger cats. A kitten’s teeth first come in between two to four weeks; their more permanent set appears at around four months of age. If you open a cat’s mouth and find permanent, white teeth, the feline is likely to be around a year old. Some teeth yellowing might place between 1 and 2, and tartar build-up on all the teeth indicates that the cat could be between 3 and 5. Missing teeth may indicate you have a senior cat.
Muscle Tone: Younger cats are more likely to have some muscle definition from their higher activity level. Older cats are usually a bit bonier and may have some extra skin hanging or protruding shoulder blades.
The Coat: A younger cat usually has a soft, fine coat, whereas an older cat tends to have thicker, coarser fur. A senior cat may display grays or patches of white.
The Eyes: Bright, clear eyes without tearing or discharge are common in younger cats. A cat with some cloudiness in their eyes is likely to be 12 years old or so. While inspecting the lens, also examine the iris of the eye. Young cats have smooth irises, while the iris of a senior cat can sometimes appear somewhat jagged
Info for this post from catster.com