Why is Aldi asking me if I'm over 18?

OK, what's going on at Aldi? At our local store, every single person who buys alcohol, regardless of obvious age and stage in life, is asked whether he or she is over 18*.
We mean even the obviously pensionable. We mean even those of us with a couple of kids hanging off us whose grey roots really do need attention (ahem...). We mean men in flat caps and women in rollers and housecoats. Everyone.