Different species may have different ages of brain maturity at which point alcohol won't pose as much of a risk of stunting their mental development. Elves for example settle into adulthood at around 100 years of age.
So a responsible legislature would codify in its laws what the minimum drinking age is for each species based on science's best understanding of their physiology.
Not really a good analogy, because the age at which you can drink is based on where you are, not in where you were born etc. An American 18 year old could go to Canada or well pretty much anywhere else in the world and they can get as drunk as they like.