How come 18 is a adult but still has teen in it?

Question

When are kids adults? I know 18 is legally and otherwise considered a adult but why does it still have teen in it and 19 has teen in it except for 20? I always considered 18 a adult when I was young but parents always said your still a teen 19 has teen in it? When I had a child at 19 and was working and lived away from home. 
What’s your thoughts?

Answer

You don’t have an adult brain or body till 25. So I would consider anyone under 25 a teenager or young adult, but definitely not an adult. I don’t care what the law says 🤷‍♀️ if your brain isn’t equipped to make good choices, you aren’t an adult.

Answer

Because 18 and 19 are numbers with the word TEEN in them, that’s where term teenager came from

Answer

I consider 18-22 “young adult”, it’s that coming of age time where you’re expected to be figuring things out. You may be in college, getting your first job at some crappy place, not have health insurance, your car may suck... like you’re not where you will be for the rest of your life. Maybe your parents still pay your cell phone, maybe you still live with them. So I don’t really consider that full-on adulthood just yet. Legally you’re entering it, but it’s that first step. It’s not all the way there. Some people mature faster but it’s still the grace period. If you’re a mess at that age, it’s fine. If you’re a mess at 33, it’s like ... oh girl.

Answer

If I look back at who I was at 22 I was still pretty stupid....I can see how 18 worked in the 1920's to be an adult, but in my time it is a bit after the 20's for most.