Hi,
In my native tongue, 'girl/boy' is the preferred term when it comes to referring to (fe)males from ages 16 to 30 (sometimes even 35). It is stricter with girls.
If you call a 25-year-old a woman, she will feel ****ed-off (as she will (righteously) suppose you have meant to imply she looks older), if you call her a lady, she may slap you right in the face (and most bystanders will applaud her), as lady is strictly reserved for 75+ old women and otherwise considered a pejorative, misogynistic offense.
I have hardly heard any of my male friends at home referring to themselves as men unless one is into toxic masculinity and wants to stress how manly he is, although there are better (and less chauvinist sounding) ways to emphasize one's virility.
I am sometimes surprised when I hear British students referring to their boyfriends as men and, when I ask how old the person is, am told '19' or '21', which forces me to burst out laughing. Boys at UK unis, however, hardly call her gfs a woman.
Why is there such a difference in the UK that being called a girl is considered perfect for less longer than a boy? Is boy considered a diminutive term or is masculinity simply overrated as the majority of British still seems to cling to traditions (even those on the left)?
Thank you for your clarifying advice.