When you hear a song on a "classic rock" or "oldies" station that you clearly remember when that song came out.
If you still think it's weird that 6 year old kids have cellphones.
If you still say "interweb" when you refer to the internet.
If you still use America Online and think it's better than a basic web connection
If you still pronounce http:// when you're giving someone a website URL.
If your hair is white and you're not an electrician.
If you've ever said "new fangled".
If you remember when your normal bus route was served by trolleys that seemed to spook the horses.
If you still call black people "colored" and don't understand why people see anything wrong with that.