But next year he will be a 5th year varsity player! IJS and I know he played Varsity as an 8th grader.
You make a good point - it's public knowledge that he played for Red Lion's varsity as an 8th grader, so this year would indeed be his 5th season of playing varsity football:
Since the following MPSSAA rule would appear to limit students to playing 4 seasons of eligibility in any one sport, how is he eligible to play next year?:
Student eligibility for participation in interscholastic athletics at the high school level shall be based on the following criteria:
D. Students may participate in interscholastic athletic contests for a maximum of three seasons in any one sport in grades 10, 11, and 12. Students who participate on an interscholastic team in grade 9 will have a maximum athletic eligibility of four seasons in that one sport.