Gosh, this thread is eye-opening! 😀
I'm mid-40s and men offering their seats or opening doors for women has always been a thing as far as I've seen. Not every man does it, of course, but it's very common where I am in NI. My dad always did it, my brother and husband (both 40s) do it, colleagues, strangers etc., and I am teaching my 10 year old son to do it. Why? Well, these days I really do think it's just taught as good manners, without any deep agenda.
My parents were very emphatic that it showed respect for women. I think there's a lot of truth to this and it's a bit of a stretch to say any man who does this holds sexist views or expects traditional gender roles. In the case of my own family, male friends and colleagues, that's definitely not true. It's kind of sad that people are so suspicious of everyone's motivations these days.
I totally understand able-bodied women thinking it's unnecessary, and I sometimes politely turn down the offer myself, but it's nice to be given the choice. I was also taught to offer my seat to anyone else who might need it (whether men or women).
But there's so much physical and sexual violence against girls and women these days, that a gesture of courtesy from men to women (however small) is ok with me.