I got carded at the gas station where I buy my smokes for the first time ever. I've been getting smokes there for the last 10 years. The cashier was new and said I looked younger than 27. I said thanks because I AM 27!!
Under 40 is Walmart's policy I believe.
I've also seen a elderly man that looked more like he was in his late 60s get carded in Walmart before. I thought to myself "REALLY?!"
I believe under 27 is this local gas stations policy unless they know you really well, which all of the cashiers but this one does.
Anymore it varies from place to place though I think the federal law is if the person appears younger than 25 they must get carded.