If a teacher behaves like his students, actually I find it hard learning anything during his classes then. Because he skirmishes too much with the students.
Nothing against if you find a teacher who's already that old that he can say about my musical preferences "hey, fuck, didn't heard that stuff for 20 years!", that's just a stone in the wall, if otherwise he shows signs of a typical adult, distance towards his students and a greater personal difference to them.
But teachers which you can hardly distinguish from their students in attitude, that's horrible, you hardly learn anything from them. They're more the type of people which you wanna go binge in a tavern with.