I still wear my skinnies because they were more slim than skinny anyway- I never seemed to be able to keep jeans particularly tight, even jeggings, they always bag on me. One good strategy if you still like skinny/slim jeans is to change the colour, I've a lovely pale blue pair, not too tight, and I wear them in the summer, my teenage girls think they look ace, also with Victorian type of boots in winter.
I don't think a lot of the things mentioned on here are really that dated. No-one is going to laugh at me going out of the house in slim jeans as opposed to boyfriend jeans aged 50.
I think the most dated thing is probably footwear, not clothes. I don't wear New Balance trainers as they would look ridiculous on me, but on my girls they look great with midi-dresses.
I rarely think people look very dated these days, though, they may not look the height of fashion, but I don't gasp at people wearing leggings and a rain-jacket, walking the dog, or jeans and a t-shirt, it's just not terribly startlingly awful. I'm trying to think of the last time I saw something very dated- my teens would say the heavy-make up fake look has dated quite a bit now, that's not what they aspire to (they prefer the 'clean' aesthetic), but most women a bit older in the public eye still go for it and Love Island is wall to wall fakery!
I still wear low heels though, chunky boots etc, so what would I know! Bought mostly in the past two years, amazing how you can still get this dated stuff everywhere...