How did the government or modern society choose 18 as being the age of beginning adulthood?

Question

Is there a scientific explanation? Like its the age when our bodies stop developing.

Answer 1

Until the mid-1960s, American society conventionally viewed 21 as the most appropriate age for full adult status, as reflected in most state and federal laws. The Vietnam War brought the age of majority status into the spotlight. Eighteen-year-olds were sent off to kill or be killed, but they could not vote. The result was the 26th Amendment to the United States Constitution, which lowered the voting age to 18 for all elected positions, federal and state. After the 26th Amendment was ratified in 1971, it seemed logical to change all minimum age limits to 18. Most legal minimum ages are still at 18. But, there has been one significant exception: In every state in America, the drinking age has been raised from 18 to 21. Because casino gaming is usually associated with the availability of alcoholic beverages, most states put the minimum age for gambling in a casino at 21. Casino-style games, including slot machines, are also the most dangerous forms of gambling.

Answer 2

it is the age that most people have left puberty and stopped getting taller.

Answer 3

Andrew K's response good.  Biologically, adulthood is generally achieved at 21.  At 18, the brain is still developing, hence the risk taking behaviour etc etc evident.

Answer 4

So they could get kids the h**l out of the house.

Answer 5

I don't think there's any scientific reason behind choosing 18 since all people develop differently.  I'm pretty sure it's just an arbitrarily chosen age like 21 for alcohol.