I don't know of a minimum. Pretty sure I mentored down to like lvl 6 to help someone level. But then again, I was not aware you could even have a level 1 toon. I thought everyone started out lvl 2 because you gain enough xp in that tutorial to level. That not the case anymore? Been a while since i rolled a new toon.
-h
Fae's do not have a 'noobie island' and you can meet up with them at level 1