The U.S. has not always had a uniform drinking age. Following the repeal of Prohibition in 1933, most states originally chose 21 as the legal standard.
Across the globe, the legal age required to purchase alcohol varies significantly, reflecting diverse cultural, historical, and public health perspectives. In the United States, the minimum legal drinking age (MLDA) is strictly set at across all 50 states. While this is one of the highest limits in the world, many other nations—particularly in Europe and the Americas—permit alcohol purchase at 18. The United States: A History of the "Age 21" Standard
History of alcohol minimum purchase age by U.S. jurisdiction
The Minimum Legal Drinking Age: A Global and National Overview