"Have you ever used Microsoft Encarta for your homework?"
"I have no idea what that is"
This was on the Greg James show (1h22m in) which occasionally tries to guess the age of a random phone caller. You could do quite well with that question - if they answer yes, then they're a child of the eighties (as Encarta was the reference source in those pre-Wikipedia days). If the answer no, then they're older. If they haven't heard of it then they're part of the iGeneration.
And the answer for that caller's age? 19!