When you go into a store--thrift shop, used furniture, etc--and discover that the mixer/serving dishes/utensils you bought as a bride have now been upgraded to "Vintage".
When an old classmate recognizes you and you not only have no idea who he/she is (even when they introduce themselves) and you realize that he/she thinks you're someone else...even when you introduce yourself back, and they say, "no you're not"--and now you are suddenly in a world of alternate universes
The books you loved as a child are now in the category online of "collector's items"
Everyone you went to school with, were a bridesmaid for, or you threw baby showers for, is a grandparent. They are suddenly old. Too.