Why Is the Age of Adulthood 18 and Not 21?

Answers to your questions about the news.
April 23 2013 7:37 PM

Old Enough to Vote, Old Enough to Smoke?

Why are young people considered adults at 18?

Women smoke in a Times Square pedestrian island on September 16, 2010 in New York City.
Officials in New York have proposed raising the minimum age for purchasing cigarettes from 18 to 21.

Photo by Spencer Platt/Getty Images

New York officials proposed Monday to raise the legal age to buy cigarettes from 18 to 21. In 47 states, the age of majority—the age at which a person has the legal rights and responsibilities of an adult—is 18. Why is 18 considered the age of adulthood?

Jennifer Lai Jennifer Lai

Jennifer Lai is an associate editor at Slate.

Because that’s when people get to vote. Suffrage has long been tied to adulthood and the age of majority in the United States. Before the passage of the 26th Amendment in 1971, 21 was the minimum voting age in most states—and thus served as the age of adulthood in most areas of law. Congress lowered the nationwide voting age to 18 as a response to unrest and passionate debate about the Vietnam War. Many felt that those who were old enough to be drafted into the armed forces should also be able to vote. Retaining a higher age of majority didn't seem to make sense if lawmakers were going to let young people vote at 18, so states began using 18 as the new measure for legal adulthood.

But why 18 for the voting age—and not, say, 16 or 19? It’s pretty arbitrary: There’s no scientific basis behind the age itself. Although one might assume that most 18-year-olds have reached maturity, researchers have shown that adolescence actually extends into the early 20s. Prior to the 20th century, the age of majority didn’t carry much significance: Teenagers were routinely elected to British Parliament, 5-year-olds could sign binding legal contracts to work until the age of 24, and 8-year-olds could be executed for arson.

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There’s no clear reason why 18 was chosen for the minimum voting age. Some historians point to the development of the education system and the expansion of high school and college enrollments. By the 1960s, attending high school was a near-universal experience among American youth, and most students graduated from high school at age 18. Other cultural shifts in the ’60s and ’70s changed the way Americans thought of youth, making them seem more adultlike. Young people in the Vietnam War era appeared better educated, more politically active, and thus better prepared to take on adult responsibilities than those of previous generations.

So if 18 is the age of adulthood, why is 21 the legal age for consuming alcohol?

Because teenagers were shown to be responsible for a lot of drunk driving accidents. When the 26th Amendment lowered the age of majority, many states experimented in the 1970s with a drinking age below 21. They changed their minds quickly: Accident statistics in those states showed a substantial jump in the number of drunk driving accidents involving 18-to-20-year-olds. Groups like Mothers Against Drunk Driving played a key role in lobbying for the National Minimum Drinking Age Act, which was clearly an anti-drunk-driving measure. When Congress passed the act in 1984, every state was effectively forced to raise its drinking age back to 21.

Explainer thanks to Timothy Cole of Temple University; Elizabeth S. Scott of Columbia Law; Daniel T. Cook of Rutgers University; and Holly Brewer, author of By Birth or Consent: Children, Law, and the Anglo-American Revolution in Authority.