That's exactly right Trade, the cashiers in liquor stores and now some supermarkets are legally obligated to request to see your ID regardless of your age, and if they are caught not doing it, they can be fired because the store owner doesn't want to be liable for selling to those who are not legally able to purchase.
Only recently they started selling full strength beer at Walmart and local supermarkets, I picked up some Miller High Life and the cashier asked me if I was over 50, I told her yes, I'm 66. She said she had to ask that question if there was any doubt, and I have no problem getting out my driver's license if needed, so the employee doesn't get into any trouble. Not a big deal, it's the law. Just so happens that in Walmart, over 50 verbal validation is good enough, at least at my local store.