IME, in the Chareidi/Jewish world adult women are very infrequently called girls, and it is wrong to call them that IMO.
About “older” singles, I think any age above the higher end of that particular communities general marriage age range qualifies for that term. A chosid might be called that by 22. For a yeshivish fellow that might be 25. For a member of the MO community it could be 28. And for a gentile it would be higher.