How to age a rodent i want to know so i know how long he have to live?

i got my male gerbil 3 weeks ago, and i was of late wondering how old is he?
does it depend on private part size or look?
(i know, kinda weird)
please help!

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Answers:    Generally rodents are aged by their teeth (in certainty, a lot of animals are). Teeny little white pearls, and you've got a real teenager. Long, yellow teeth, an oldster. The amount of wear on a gerbil's teeth is also a good clue to age.

A healthy gerbil (which is in actual fact pretty rare, but if he hasn't exhibited any health problems surrounded by the past 3 weeks, you've probably got a healthy one) will live approximately 5-6 years given the proper care, and some have reached elder (I had one that was almost 9). So, unless you get an old gerbil, odds are you'll have frequent delightful years with your little guy.

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depends on thier teeth
when ther older they will draw from big and yellowish

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