From Rule 16
Once the school determines that a student is promoted from eighth grade, high school eligibility begins immediately in the following
semester. A student shall not have more than eight consecutive semesters of possible eligibility in grades nine through twelve, regardless of whether the ninth grade is included in junior high or in a senior high school

I would interpret that if they pass eighth grade, their eligibility starts then. If they repeat seventh grade 5 times(sarcasm), as long as age works out they are fine. If they fail eighth grade first time they are fine. At least that is how I am reading it. I could be and probably am wrong in some way shape or form.

Eric