Field owners/operators trumph "group leaders", every time and every day, full stop.
Field owners/operators run the field, set things up, set the rules, and take on the risk of operations. "Group leaders" organize players, nothing more.
If your "Group leader" wants all-ages - then tell him to have at it - on his own field. Not yours.
Set some standards, and your field standards and player base will improve. Making it an all age shit-show, and it will just dilute the player base to the point where the quality players get fed up and go else where, while you are left with a giant pile of aggravation to deal with.
You are there to have fun, as well as organize the field - you aren't having fun if you end up running an airsoft day-camp.
It's time to stage a Coup on your "group leader", and tell him to get stuffed.