One problem with getting older is that perfectly good lesson plans are going stale. For instance, I've been teaching game theory since 2007, when it was completely reasonable to refer to the 2001 film A Beautiful Mind. I mean, my copy of the book has the movie tie-in cover. How old can it be?
A few weeks ago we got to game theory in class. I mentioned that the Nash equilibrium was named for John Nash and is featured in the movie. I asked, "That movie's not too old to expect you to know it, is it?" One of my students said, "It came out before I was born, but I know that it exists."