How can you tell a guinea pigs age?

Question

How can you tell a guinea pigs age?

Answer 1

do you take him/her to the vet?  they can probably tell you by the teeth...that's usually how they age dogs and cats...

Answer 2

Usually you can guess by their weight, their eyes and nail length. Their teeth are constantly growing so you can't tell by teeth.

Answer 3

cut it in half and count the rings!