Its not only the under age person getting hurt, but what if an underage person shoots a hiker, or somebody not involved in the game. Its more likely that the organizer will get the law suit.
Bottom line, there have been many posts like this in the past concerning under age players, organizers can set the age limits at 18, or 48 (which means only Woody would play) but its THEIR decision, not mine, not yours, not your parents.
Taz, I think you did the right thing 100% you made a rule, you published it clearly, and you enforced it. Its guys like you that keep the sport safe. Once you bend on one rule, all safety has gone out the window.