Am I the only one who automatically reads "FTL" as "Faster Than Light"?
I read "FTL" as "Full Transit Liability"

At the end of the day, store policy is store policy. If the manager tells you point blank that you must ask every customer if they are over 21 then you don't have much say in the matter - it's not being a jobsworth. It shows a little inflexibility on Managements part, but the blame for this should in no way lie with the cashier.