I work pouring samples of alcoholic beverages in retail stores. Yes, I've had a few people get upset, but the policy is that I have to card EVERYONE, even my own mother (and yes, I will tell people that, it does help calm people down "I have to card my own mother, and I've known her all my life. She gave me the "Mad mother glare", but....).
Your employer may have a policy that says if you can tell their old enough (like 40+), you don't have to card them.
I'd play it safe though. Remember, if a minor makes a purchase YOU get a criminal charge; the store gets a fine; and your boss my fire you.

