I meant it as the company policy dictates you show it, not worldwide or country wide or state wide. As far as I know it's completely optional worldwide.
I'm almost 18 and look much younger. Some days I get my ID checked to get into rated R movies. Other days I get away with buying pool chemicals that you have to be 18 to buy without having to show ID.
Teaspoons though? That's ridiculous.
A few days ago I got IDd buying an M rated video game. And I'm 21. I don't know how he thought I looked 16 or under. I think it just depends on the person who's there.