Final answer:
In most states, you must be 21 years old to purchase alcohol due to the National Minimum Drinking Age Act of 1984.
Step-by-step explanation:
In most states, the legal drinking age to purchase alcohol is 21 years old. This age requirement is a result of the National Minimum Drinking Age Act of 1984. The act mandated that states raise their drinking age to 21 or risk losing a significant amount of federal highway funds. By enforcing this age restriction, the act aimed to reduce the incidence of drink and driving and promote responsible alcohol consumption.