Most of today's readers know that the legal national drinking age is 21. But do you know why? If you don't, that's okay. Few know that the age of 21 was set on July 17, 1984 when then President Ronald Reagan signed the National Minimum Drinking Age Act. The act allowed the federal government to withhold funding for highways from any state that established a drinking age less than 21 years old. In the last 31 years, no state has dared to oppose it.