system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How were the 'adult' ages of 18/21 established in the western world for things like voting, drinking, legal liability, etc.?
gpt
21 was first for voting decided at the framing of the US. It was figured that you were likely married and might start owning land that young. It likely also flowed from the British system. Eventually states started making drinking (generally 16-18) and legal adulthood laws(generally 18-21). The military started bringing up their minimum recruitment age to 17 with parental consent and 18 without. Prohibition made alcohol legally banned so when it came back, the rules were generally stricter than before with most states setting it at 18 for purchase. During the Vietnam war many 18-21 y/os were serving, but missed out on the election. Massive protests and activism led to the 26th amendment bringing the age of voting to 18. Shortly after it applied to all local votes too. Mothers Against Drunk Driving started a campaign to reduce fatalities and lobbied individual states and the federal government to raise the drinking age to 21. Many states did so on their own, but once the federal highway act funding required the 21 limit it was pretty much set in stone.