Well it's different everywhere you go. I work in a liquor store and I have to ask everyone who appears 30 or under, if anyone is questionable I have to ask. We get secret shoppers all the time (bastards) and since I get huge fines I ask pretty much everyone who looks under 40. So many people get mad at me for asking, it's stressful sometimes. That being said a lot of fat people are younger than they look so I ALWAYS ask, but they tend to get the maddest. Fit people are usually so nice about it.