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Every time I talk about jawbone aging in here, someone is inevitably gonna pop in with “that isn’t accurate,” revealing that they don’t know the method or it’s limitations. For more curious and open-minded hunters, jawbone aging is a simple series of questions. Here they are:
Six visible molars in the lower jaw?No = fawn less than 1 year old. You’re done.
Yes = 1½-plus. On to the next question.
Does the third molar from the front have 2 or 3 cusps (sections)?3 = 1½ years. You’re done.
2 = 2½-plus. Next question.
Note that so far the options are clearly evident. There’s no judgement call on these first two questions. You just sorted any jaw into fawn, yearling or 2½-plus with 100% accuracy. From here on, answers may not be clear and judgement calls may have to be made. Can you hack it?
Move on to the next (fourth) molar from the front and ask: On the tongue-side crests, is the strip of exposed dentine (dark) wider than the strip of enamel (white) on either side of it?No = 2½. You’re done.
Yes = 3½-plus. Next question.
Here are photo examples of what I’m talking about. The tongue-side crests are on the right side in both photos. The left photo is a clear “No.” The right photo is a clear “Yes.”
Move on to the next (fifth) molar and repeat the question about dentine width.No = 3½. You’re done.
Yes = 4½-plus. Next question.
Move on to the last molar (sixth) and repeat the question.No = 4½. You’re done.
Yes = 5½-plus. You’re done.
If you’re not sure about Yes or No on dentine width at any point, get opinions from others, or stay at “No.”
You cannot use this method to reliably divide “5½-plus” any further, so don’t try. Send an incisor for lab analysis on older deer.
You cannot use this method to reliably divide “5½-plus” any further, so don’t try. Send an incisor for lab analysis on older deer.
Here’s one exception to the above. On *late-season* yearlings, the permanent 2-cusped third molar may have already pushed out the temporary 3-cusped molar. But that new one will look clean and sharp and may not be fully emerged. It’s still a yearling!
That’s the method. You don’t have to be a biologist (I’m not) to sort deer accurately into useful age categories. Just follow the steps, don’t try to go beyond the limitations, use your best judgement, and get back-up opinions if you need help. 
