To clarify here - do you think that people should be forced to leave school boards as soon as their kids graduate? Do they end up eligible again if their kids have grandkids? Is this limited to people with kids going to that specific school? Also, does paying school taxes not make you have some skin in the game?
And what about just input on the society you live in? It seems to me the solution in your example would be to have younger people run for / contest the school board.