In American English, it is acceptable and common that an older man calls a man his junior, "son"—even if the younger man is not the older man's child (or related to him in any way).
Definition of "son," according to Oxford Dictionaries Online:
1.6
(also my son)
Used by an elder person as a form of address for a boy or young man.
Example:
“You’re on private land, son.”
At the same time, I have never heard "daughter" used to address a younger woman. What is the reason for this linguistic divide?
In my preliminary research on this topic, I found a somewhat related question that was asked on the Q&A site, Quora: Why is there the phrase "son of a bitch," but not "daughter of a bitch"? The provided answer is that societies around the world have historically been patriarchal; females were regarded as inherently contemptible.
I'm not sure this explains or has anything to do with my question. I would imagine that even during the time when women were regarded as second-class citizens, polite terms for a senior man to address a girl (or a senior woman to address a woman her junior) still existed.
On a separate note, the dictionary definitions of "son" that I've looked at do not specify the gender of the speaker of this term. However, based on my experience, I had thought that only men use this term. Is there any validity to my understanding? Have you ever heard an older woman call a boy, "son"?
Best Answer
To answer your last question first, yes, in my experience it is also exclusively used by men. There are approximate equivalents for girls/women (e.g. "lassie", "miss", "darl", "hun") though none so universal as "son" that I can think of. I wouldn't be able to give a reason why.