Obviously teenager is 13-19.
“Young adult” would start at 20, but where’s the cutoff at the upper end? Similarly, what’s the range for “adult”, “old”, “elderly”, " ancient"?
If someone asks for responses from “old men”, how do I know if it applies to me?
Adult’s 25, Old’s 50, Elderly is 75, Ancient is 100.
Those of us in our late 40’s are horrified to learn this! You turn 40 and you’re “middle aged”. Ten short years later and you’re just plain old.
At least growing up is optional, even when growing old is mandatory. ;)