You could easily guess I'm somewhere in my 30's because you would see the grey and white starting to peak out in my 'stache. Russ, you're white hair free so I'd guess sub-30. Facial hair color is a much better indicator than teeth I think, and maybe that's what your rando coworker is using (consciously or subconsciously).
And yes, this might be the weirdest thread in a while. :)