I just returned last week from the annual "Guitarfest" in Belgrade, Serbia. Numerous great performers and teachers were there giving master classes, such as Roberto Aussel, Pavel Steidl, Kazuhito Yamashita, Oscar Ghiglia, Roland Dyens, H Kappel, C Marchione, etc.
I attended as a non-performing student, so I could sit in on all Masterclasses and watch/listen.
There was some sort of an application to fill out, based on the students performing, I dont think it was any problem to be accepted as a student, in general.
Students were aged about 20 years, on average
They chose what to play, they told the "teacher" at the beginning of the lesson. They typically played one movement of a longer Bach piece, eg, Loure from the E major suite (I am referring to what we consider the guitarist`s E major suite for lute, it is from one of the violin sonatas).
The teacher usually wanted to know what was the edition/who was the editor or transcriber of the piece.
About 85% of pieces were Bach (!) Related to that, there was lots of discussion on the part of the teacher, usually, about the issues involved in adapting Bach`s music to the guitar, e.g., "the guitar is between violin and organ in its possibilities for voicing..". Also, about the interpretation of Baroque music.
The teachers concentrated to about 95%+ on interpretation, not on technique.