I remember a joke that might be appropriate here:
A woman was at the dentists, and it suddenly occurred to her that she had been at school with someone with the same name as the dentist
.
"It can't have been him though", she thought, look in at the elderly, balding man who stood over her, "he's far too old, way older than I am".
However, before leaving the room she saw his certificate on the wall, and the dates made it perfectly possible that it could actually be the same person.
She tentatively said "I think you might have been in my class at school!"
He looked her up and down, thought for a moment, then asked, "What subject did you teach?"