You know you're old when:
you hear a song you grew up listening to now on an oldies station ( I did today:(
you try to figure out how to make an iphone app and all the "teachers" are thirteen year olds
Schools change the names of such things as rounding up to estimating and it confuses the heck out of you.
Classrooms focus on computer learning and you hope to God you can keep up with your kid.
The once cool dance you remember ( and now willing to teach to your younglings) would cause your child such embarrassment that they would would rather pay you off to stop doing it than put it towards the latest gadget they were saving for. ( Hasn't happened yet, but sure it will one day when I feel like causing total humiliation.)
you can't remember making plans to go out with your father for dinner one hour after making them. You even go as far as to have planned the dinner and discuss it with the kids while you are in the food store about to purchase it. ( Happened the other day.)
You can't remember anything else that makes you feel old because...well....you just can't remember anything anymore.