Final answer:
Individuals under age 18 in the United States have the lowest adult alcohol drinking rate due to the legal restrictions imposed by the National Minimum Drinking Age Act of 1984.
Step-by-step explanation:
The group with the lowest adult alcohol drinking rate in the United States is those under age 18. This is largely due to the National Minimum Drinking Age Act of 1984, which required states to raise their drinking age to twenty-one. The act enforces a legal barrier to purchasing and consuming alcohol for this group, which typically results in lower reported drinking rates compared to other age categories. However, this does not necessarily mean underage drinking does not occur; rather, it is not legally sanctioned and is less likely to be reported in adult drinking rate statistics.