+1 on that. I've learned Clojure in the past and keep wanting to go back to it but Clojure has been the hardest language for me to become fairly comfortable with. I think it may have to do with its dynamic-ness. There's basically no problem Clojure experts can't find a solution for. Its basic constructs are very powerful but all those solutions are not codified in the language itself. So Clojure has this extra layer of "culture" around it and as a beginner that's very hard to learn without a lot of doing and running into a wall quite a few times. Just when I think I have a grasp on the language, I see a new construct or new way of doing something that's completely alien to me and wasn't in the Clojure book I just read. I've not saying one can't become good at it but it takes a bit and might help to have an expert or two guiding you.

Yes, you can, if the new hire is fresh from school and is smart.

In my startup, our onboarding time is two weeks. I would say nine out of ten fresh graduates we hired picked up Clojure and were able to do something useful after two weeks. But we did have one or two persons who were not able to and they ended up in one of FAAG (yes, we did do leetcode style interviews, but only asked medium level questions).

Depends on where they're coming from. If all they know is Java, then surely not! If they've done Python and C and Erlang before, the switch doesn't seem as hard.

The GP didn't say 2 weeks to effective, it was for learning the basics. Or do you disagree with that as well?