requirement, obligatory, preconditional, pre-conditional, predecessory, precedentary, precedable, preambulatory, preexisting, antirequisite, more...

postrequisite, non-prerequisite, optional, secondary

class, test, experience, age, skill, more...

necessary, essential, important, first, indispensable, absolute, basic, fundamental, only, second, major

academic hurdle,   minimum requirement,   event requirement,   pre requisite,   academic hurdles,   needed before,   pre condition,   step to be met,   formal requirement,   required step