Hi there! Being a class helper myself, I think the requirement of level 70 is really needed. Class Helpers should be familliar with how classes work and now with all the quests you can easily get to level 40 without even having to go to too many classes (I got to level 38 on my alt within a few days only having to go to 4 potions classes and a flying class). The higher level you get, the more xp you need to level up, the more classes you have to join- Therefore, you gain a lot more experience on how all sorts of classes work and which assignments that you write get which grades.
So if you really want to become Class Helper I suggest to join as many classes as you can and try to get good grades to level up faster.