I work with plenty of men who refer to their professional female colleagues as ‘girls’. It’s especially bad when it’s referring to an all-female team, like ‘the HR girls’.
They don’t call their male colleagues boys. Children generally have lower social status than adults. Women generally have lower social status than men. Calling women ‘girls’ in a professional contexts suggests you view them as extremely low on the social ladder. It’s demeaning and belittling, and implies that they’re more naive and less competent than their male equivalents.
Some women get socialised to go along with this and only ever be nice and unthreatening in the workplace, even if it costs them personally and professionally, because shit like calling women girls pigeonholes grown women as all of the negative things society implies about very young women 24/7 – annoying, irrational, flighty, overly emotional.
Reducing some women’s status in this way can be harmful to all women – I’ve learned to be firm and icy enough at work that I don’t think anyone does this to me, but doing it to my peers devalues the status of a group that also contains me. It makes us all a bit more dismissable and disposable as a demographic.
I call my male colleagues out on this all the time and it feels like a sacred duty.