We (I'm 50+) know for sure many more things and I see the surprise of junior developers but the exact details? There are too many of them, especially because senior developers often are not narrowly focused on a single part of a project.

A simple example. I'm working with Rails, Django, Phoenix and React (3 different projects). I know I need to do a strftime but I don't remember the exact details in any of Ruby, Python, Elixir and JavaScript. I always google them or grep the source code for other instances.

Yeah, absolutely. Even more experienced folks sometimes get stuck on this. There's some selection/confirmation bias: you ask questions in chat or whatever, and there's someone who's got a lot of answers, and you're grateful and excited by the help. But you ignore all the time they were only partially right, or wrong, or -- most important! didn't even answer at all because they weren't familiar with the topic. (But someone else did answer, and also gets added to your mental "expert" list.) And of course you don't see all the things that they don't know or are struggling with. (Some of which could easily be things that seem simple and comfortable to you!)

I try to dissuade this kind of thinking when I see it: I like answering people's questions, and I take pride in knowing a lot of stuff. But there's way more stuff that I don't know than that I know. And I might need these folks' help with something I'm unfamiliar with, so I don't want them thinking they're "below" me and there's no way they could know something I don't. I'm sure they do!