Final answer:
The legal drinking age for adults 21 or older is 21 years old according to US law.
Step-by-step explanation:
The legal drinking age in the United States is determined by state laws, but the National Minimum Drinking Age Act of 1984 set the minimum legal drinking age at 21 years old for the entire country. This law was enacted to address concerns about alcohol-related accidents and underage drinking.
The rationale behind setting the legal drinking age at 21 is based on research and evidence that suggests individuals under this age are more susceptible to the negative effects of alcohol. It is believed that delaying access to alcohol can help protect young people from the potential risks associated with early alcohol consumption, such as impaired judgment, increased likelihood of accidents, and negative impacts on brain development.