How Can You Instantly Guess Someone's Age?

Is there a way to tell how old someone is without asking? One key indicator is a person's hearing abilities.

UPDATE: The mosquito tone in this video was lost during processing after upload. To check out your ability to hear high frequency "mosquito tones" check out these sites:
http://www.audiocheck.net/audiotests_mosquito.php
http://www.freemosquitoringtones.org/hearing_test/

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THE QUICK AND THE CURIOUS
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