Check the rule book. It's on the NBRSA web site. It might depend on your state laws....
In MI, I have seen 12-13 and up shooting.
At the Nationals they have a "powder Puff" match on the Wed. of the week. In 2012 at Holton, I coached and let a "Yut" use my rifle and ammo for 1 group. And he won. Jim Dyke's grandson. I think, he was 13 or 14 yrs. He was also part of the target crew. A couple yrs later he showed up at a Tournament. He was still jazzed about winning. Someone had donated a wood carving of an Eagle for the trophy. Full spread wings and all. It was really nice. I bet he will remember that for the rest of his life.