A Distinct Lack of Barbers
I'm 47 years old, and most of the people I work with are much younger than I am - often in their 20's and 30's. Cultural references that I think are universal sometimes turn out to be pretty specific to my age group in ways that surprise me.
Take something like Bugs Bunny. Most people, young and old, have of course heard of Bugs Bunny but it turns out that not a lot of young people grew up watching it. I have, and it is because of this cartoon that I happen to vaguely know some of the music to The Barber of Seville.