nowit - hello and welcome.
Unless you're wearing something completely outlandish, men generally don't notice what you're wearing. A decent top and jeans or a skirt is fine for a pub meal. Don't stress the small stuff, really.
Be prepared for no chemistry or him to turn out to be shorter or older. But then, he may be lovely. Just don't overthink things, see if you like him, if you want to see him again. And give us an update from the loo.
Stranger - Why would it make a man look like a dick to express a preference for 26-39? That's not my preference, personally, but I'd say if he said 18-25 then that would make him look like a dick. The majority of men prefer women a couple of years younger than them. Studies show the 'ideal' age (at least theoretically) is half his age plus 7 - which would be 27 for a 40 year old man.
I don't get irritated by 40 year old women expressing a preference for men under 30 - I've seen that a couple of times - or women under 30 saying they want to date men over 45. Expressing a realistic preference isn't a bad thing, just means they're probably not your type.