Why is 18 considered being adult (being able to vote) in many countries and where does this age come from?

by thomas1599
EdHistory101

I've answered this question in a few different ways with regards to the United States and generally speaking it holds for most countries.

The reply to this question, What is the history of how the number 18 was chosen as "adult" for almost all of the world? is probably the most helpful. Happy to answer any follow up questions you might have!