This sounds nuts but that's what I call them. When you walk into a restaurant and it smells weird and there are a small amount of customers AND they are all really old, you have just walked into a Zombie Restaurant.
You should immediately devise some polite excuse and walk the fuck out. My wife is getting incredibly good at spotting this right away. She just saved us from "Good Stuff" restaurant in Redondo Beach.
My hypothesis for the reason this is the formula is first of all, not very many customers because it sucks ass. Second of all, only the customers that can't taste or smell a god damned thing anymore are left over and are not very self-aware, enticed by the lunch special alone and they just happened to be very old.