Irrelevant.
Rules are there to create an even playing field and a fair competition where no player or team gains an unfair advantage.
Its about as simple as that.
NOTE: the following is regarding week in, week out school competition. Not representative honors.
Actually SLV, it's not as "simple as that" Each child attends school for an education first. Just because one child did not achieve the academic potential by a specific date, is it your suggestion they be excluded from participation. Think about the emotional damage that could place on a child at possibly the most stressful time in their young lives (i.e HSC)
Speaking from bitter experience, even 1st XV players get bullied. And it wouldn't be a stretch that some kids would simply have a go "You can't play because you're too old and dumb" Or is it ok as long as they don't play 1st or 2nd XV. Think about the ramifications of a player like that play 3rds.
The fact this is all out on a Couch Coach's forum means it would have been fully canvassed by all CAS schools, headmasters and actual coaches. Whatever is on the website, I'll bet you a lawyers long lunch that there's so much we don't know. So speculation on the black and white of said rules is futile, at best.
