Alrighty, here's how we voted it in my realm (which i don't think we follow anymore since i stopped showing up):
From 8-13, as long as you had a parent actively fighting on the field, you could fight. You had to stay with your parent, and if he died you died. We did this b/c we had too many parents using us as a babysitting service, and many of our vet's were complaining of hobbits cheating shots, etc. The games stretched out much longer, because they would run around forever and never fight.
14-16: your parents had to show up to one practice, but didn't have to fight.
16+ was what we established as "adult" for fighting.
it worked, and we ahd the hobbits fighting each other off to one side. every once in a while, we would do team battles, with one side figthing with the "hobbit army" (we had like, 12 hobbits at one point)
thats my 2 cents