There is a whole genre a jokes around the theme: you know you are old when…

One of my favorites has been:

You know you are old when the music you listened to is now called classic rock.

Or another of my favorites:

You know you are old when kids start calling you mister.

The other night, while watching TV, I came up with another:

You know you are old when Target stops marketing to your demographic.

Cheers!