You can get married at 16, but can't buy a set of cutlery to eat with in your new home, nor paint & solvent to decorate it unless you take your mum or dad with you to buy it for you, after saying it is for themselves!
You can join the army at 17 and learn to fire a sub-machine gun, but you can't buy a pen-knife. You can fly a aircraft solo at 17, but can't buy petrol to re-fuel it after getting a full pilot's licence until you are 18.
The law is clearly as ass.
The retailers do have a problem if they don't check, but when those checks are stupid it is simply insulting. Best then to walk out and if you have a shopping trolley full of goods which might include a 4-pack of beer, they will have to put it all back on the shelves .
I'm still waiting to be asked, but then .............. one lives in hope!