At what age does a child become a woman of a man?
There are a few cultures that mark that time in teen-age years.
Most European cultures marks the age at 21 years.
I got to thinking about the span of the human life.  These days’ people are living into the late eighties and nineties.
It you are considered an adult at the age at 21 and you live well into your nineties that means you are and adult for 70 years.
Society considers a person is getting old in there 40’s. If you life into you 90’s that means you are old for 50 years.
So you are a child for 11, years, teenager for 7 years, nothing for two years,(19 & 20) adult for 19 years and old for 50 years.
There is definitely some thing wrong with the calculation and definition of each stage in a human life.