Why are you this way?
It's the internet, where comments remain in perpetual purgatory. Considering that you lack the ability to understand how definitions work, is no surprise you are found lacking here, as well.
I can see that you believe the world revolves around your perspective (it doesn't). How you personally define age groups, with your rigid categorization, is not how the larger world views this, nor how the accepted definitions are determined.
(TLDR: Your world view is only your own, and you don't matter in the larger scheme of things. Get over yourself.)
"nor how the accepted definitions are determined"
So you can call anyone a kid even if their age number blatantly says that they are not a kid.
That's something.
I'm pretty sure i didn't define these age groups i just searched on the internet about them. (And age groups might be rigid but maturity is not)