No. I think it's patronising.
Why should 18, 19 and 20 year old tax payers be restricted from 'adult' activity?
I've always thought the American practice of infantilising grown men and women in this way to be bizarre. by 21, some of those women whill have been fertile for 10 years, they are biologically PAST their most fertile time, they are the same age at which we start serving on a jury in this country, they are 5 years older than the age at which we consider ourselves sexually autonomous..... so we can get married, but we can't have the champagne party until the child we conceived on our wedding night starts school.
Does this sound remotely sensible?
You cannot control someone's sex drive with the law. If yo9u are allowing people to have sex, you are saying that you consider them old enough to have and care for a baby. If you then say "But you can't drink alcohol for another 5 years" what are you saying about the cherishing of babies in your society? When teenagers and young adults are raising families but may not crack open a bottle of white at the end of a hard day doing so? When a shop manager can walk into her own flat after a hard day of organising her staff and has the options of tea, coffee, or milk? No beer, no wine?
We should not be following America on ANYTHING to do with food or drink, did you see Jamie Oliver's crusade into Huntingdon - and what he found there?
As I once saw an old fat French man declaim - "America! Pah."