I've never been called "Mate" but nothing wrong in anyone saying, "I'm seeing/going out with my mates", if they want to. My husband used to call our pets, "Mate", when they jumped all over him & "Come on mate, lets go out for a walk".
I've heard "You guys" and "These guys" for as long as can remember and see no problem with it. As for Rhod Gilbert saying 'posh' people use the word about their kids - I reckon he made that up. Annoys me when people talk about others as 'posh' especially when they're not - who is 'posh' anyway? I wonder about the woman in the Guardian link, has she nothing else to think about.
I did speak to someone once quite strongly at work about referring to a group of young women as girls in a patronising way, with stupid grin on his face. "How are you today girls?", "Have a nice evening girls". They didn't like it. However I have two daughters who are young women (and are my girls), they go for a night out 'with the girls' and have 'girlfriends'. As did I and still do occasionally.
How words are used and who uses them is key here. Once had a neighbour from Manchester who called me and prob'ly everyone else, "Love" which I found irritating but he was such a nice person, I stopped being irritated. Likewise a young woman who works in a post office which I go to sometimes always says, "My dear", which sounds quaint from someone of her age but she is lovely.
Darling is fine when reserved for loved ones.