No person under ____ years of age is to be served an alcoholic beverage on a Frontier flight.

The correct answer is that no person under 21 years of age is to be served an alcoholic beverage on a Frontier flight because the legal drinking age in the United States is set at 21 years, as established by the National Minimum Drinking Age Act of 1984. This federal law mandates that establishments, including airlines, are prohibited from serving alcohol to anyone under this age. Frontier Airlines, like all airlines operating in the U.S., must comply with this regulation to ensure responsible service of alcoholic beverages and adherence to national laws regarding alcohol consumption.

Understanding the regulations surrounding the legal drinking age is crucial, particularly for airline personnel who must verify the age of passengers wishing to consume alcohol on flights. This contributes to the safety and legality of services provided on board.