I don’t know if this is a cultural thing, but at least in California I hear the word “boys” used to refer to grown men pretty frequently.
https://en.wikipedia.org/wiki/Boys_from_the_Blackstuff
'American Red Cross – Our boys need SOX' :
https://propagandaposterstore.com/product/american-red-cross...
'Old boy' :
https://dictionary.cambridge.org/dictionary/english/old-boy
edit - could also just go straight to the entry for 'boy' :
'a male child or, more generally, a male of any age'
[1] https://www.insidenu.com/2017/8/30/16200774/northwestern-foo...