[BasDirks]

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".

[toothbrush]

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.

[BasDirks]

Please read carefully, as I stated "mixed group". How about "jongens, kom", to a group of boys and girls? It's common.

[toothbrush]

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.

Disclaimer: i have a penis.