I agree that having an age-related cliff edge is unlikely to be a good thing.
Especially as unless your DC is one of the oldest in their year (and none of their friends have older siblings) then they're going to be able to get hold of alcohol and be at events where it's flowing freely before they are 18.
Relationship with alcohol starts young - by seeing how parents and other adults use it.
I've always majored on the thought that the best way is to find your happy place and stay in it. But that everyone makes mistakes whilst they're finding that out, and it's not the end of the world. But that no-one should be blind drunk in unsafe places, so always, always, always look out for your mates.
Also risks of spirits (when I was a student, spirits were relatively much more expensive, so a bottle was maybe a once-a-term treat) - get them, if you can, to prefer wine, beer or cider, because stomach/bladder capacity is likely to kick in before harmful levels are reached.
My DC had champagne as toasts at weddings, and maybe a drink at Christmas from an age that MN would frown on, but the French probably wouldn't mind. Wine from 16 (which is the age when it's first legal for it to be served to them in public with a meal)
But I think the key isn't the precise age you allow what. It's what you model to your DC and how you communicate