These are all used this way. “Man, was I thirsty …”, “Boy was I tired …”. Or in the case of “brother” more of an exclamation of frustration. “Oh, brother!”
I don’t think there’s anything similar on the female side.
I wonder what the origin of this is (and whether there’s anything similar in foreign languages).
“Girlfriend, why you trippin’?!”
“You go, Girl!”
No connection. In those cases an actual girl is being addressed and referred to.
I say this to my gay best friend all the time.
I assume you’re jokingly referring to him as “girl” or “girlfriend”. If not, then you’re an outlier. The meaning of “girl” and “girlfriend” in those phrases, as commonly used, refers to the person being addressed.
In the examples I gave, the terms don’t refer to any person, and have no particular meaning at all other than as intensifiers/exclamations.
I do say it jokingly and I concede your point - I can’t think of any such examples in the other two languages with which I’m familiar.
Do people who do not have brothers say oh brother when they’re frustrated?
Dude!
In each of your examples, you could replace the male word with “God” and it would make just as much sense: “God, was I thirsty …”, “God was I tired …”, “Oh, God!” That makes me think that they may be Minced Oaths.
You could also replace it with “Fuck” or “shit”, so the use of brother, man and boy, could just be cleaned up swearing.
That’s what minced oaths are.