Throughout your life, you’ve developed as a person, who you were 10 years ago helped form who you are now. So by now, you’re who you’re supposed to be at this time. Of course, change will happen, by the time you’re 40 you’ll be a much different person. But, you do not just change on the dot because you’ve turned 18. No, over these 18 years, you’ve already changed for now.

Also, your question of “why 18?” is an interesting one, but also largely pointless. (No offense). If it was 19, we’d ask the same, if it was 20, we’d ask the same. While we may rid one question, along comes another. But to specifically answer, 18 is the voting age. And given that the United States is heavily driven on politics, this would make sense. Furthermore, in different areas of the world, I’m certain that this age varies and rightfully so, the rest of the world wasn’t built the same as the U.S. Politics, largely, haven’t been a driving point in the originations of other countries. (Generally)

Best of luck to you! Adulting is a hassle, but like anything, it has its moments.