There could be differences. In my language, a boy can be old enough to have a goatee. Is that the case in English?
Can a 19 year old high school senior be called a boy?
Rover makes a good point, because it's really a cultural question — and a very difficult one.
In general: Men have goatees. Nineteen-year-olds are men and women.
In the US, Nineteen-year-olds are often called boys and girls, but you can offend them by doing it. Sometimes the insult is intentional, sometimes not. Some people are offended and some aren't.
Here, it's widely considered racist to call adults, including young adults, boy or girl. To Black men,
boy is expecially provocative.
In all races here, many women resent being called
girl because it diminishes them. It tells them they're not being taken seriously. So calling a Black woman a
girl is a double problem.
In the US, when it doubt, it's always fine to say
young man or
young woman. Always!
I believe most of this applies to other countries, too, but I'll let them speak for themselves.
