What would happen to the landscape of elite level lacrosse if lacrosse followed soccer and switched to birth year instead of grade? Imagine, you could never use the “hold back” excuse when you lose. Parents would stop intentionally making their kids repeat grades to give them a competitive advantage in lacrosse (I know, I know, little Billy wasn’t held back for athletics, it was about his education and maturity level). All teams would then be on a level playing field. Soccer got it right. You can play up, but you can never play down. Lacrosse is so backwards. In most sports the best kids play up, in lacrosse they play down to stand out.
I think birth year for club lax, or club any sport for that matter makes 100% sense. School teams should be by grade obviously as that's how the kids are already grouped. If it is not a school team, there is no reason to use grade...very arbitrary measure of athletic ability and physical readiness. Also, this way kids naturally get a wider array of teammates.