In Dutch, "jongens" (boys) is very common, even for mixed age and gender. However, jongens taken literally means "young ones", so it's actually very general. Use of "mannen" (men) among a group of adult males is usually actually more ironic than the more general "jongens".
Native Dutch speaker here, and i beg to differ: i would be very surprised if someone said "Daar staat een groepje jongens" (there's a group of jongens) and meant a group of girls. "Jongens" is definitely masculine.
I probably worry about this a bit too much, but broadly speaking i try very hard to de-gender my language where possible. E.g., i avoid saying "hey guys" and using 3rd person pronouns other than "they" when referring to undetermined people (such as "the user" and "they" in a technical manual). Therefore, no, i would not find it natural to say "jongens" to a mixed group of people. I used to have a boss in a dev team who always started his emails "Heren, ..." (== gentlemen) which irritated me no end. Apart from the fact that it sounds like a toilet designation (another pet peeve: why, in 2015, do we still have binary gendered public toilets?!) i found it incredibly exclusive language.
But indeed, perhaps this is outlier behaviour and others pay less attention. I suppose it's a tic i have because i'm in such a masculine-dominated field -- i try not to make it worse by talking as if i expect everyone to have XY chromosomes.
It's not uncommon in sports. That's the kind of thing I'd expect to hear in the locker room or on the ice when playing hockey. I don't feel like maturity plays into it there. It's almost a term of endearment.
Yes, I am aware. But then again I phrased my original statement to show that there was a small frequency of use of these terms. Where females (in my area) have a very high frequency of referring to each other as girls. Almost like "woman" is a formal term.
interestingly this might be because girls like to retain some semblance of youth.
anecdotally my girlfriend (Russian if that makes any difference) absolutely hates when I refer to her as a young woman, or use the word "woman" at all. She much prefers to be referred to as a girl.
I have no issues with being called a man.. not saying that this pattern is everywhere but it's very apparent with her and her family.
No critical thought here is necessary, I suppose? It just... so happens that women "like" to look youthful? Maybe it's biological? Just the natural order of things? I am reminded of the ads from the National Geographic I own from 1940.
but "Mister" is not "Man" even my girlfriend doesn't mind being called "Miss" or "Ms", she might take exception to "Misses".. but I don't think anybody assumes at her age anyway.