RF
I think any bochur under 20 doesn’t belong in the Mir because it’s simple huge and way too free and many bachurim go there too young or simply unready for the environment and instead of shteiging end up having a big yerida there. Even if you are 20 you shouldn’t go to the Mir unless you are ready for intense learning at a fast pace and you are going good with a serious group of learners. Mir is a place for established guys.