When are you an adult?
18 or 21
Guns vs. liquor vs. driving? Voting, marrying, age of consent?
Life is complicated.
If you murder someone at the age of 18 years plus one day, the courts will see a difference versus murdering someone at the age of 17 years, 364 days. Same if you sign a contract, have an auto accident, get drunk in public, or try to vote.
There is no specifically protected right to drink or to drive on the roads, and I was driving around our farm at about 13.