RE: age for starting to shoot
I guess I was about 9 or 10 when I first started with an old Win. 22 bolt. The very first thing I got, tho, was a schooling on gun safety and proper usage. Muzzle direction, backround, loading & unloading, and learning to treat a firearm wiyh respect. If you always consider a gun to be loaded, you will be much more careful with it.
My grandson is 6, and I'm going to start him with a BB gun this summer. A few years of schooling and grasshopper hunting with that, and I'll consider moving him up to a .22. I bought a "Chipmunk" .22 rifle years ago, just anticipating this to come along. I think proceeding rather slowly and reinforcing the principals and ideas you wish to instill in them is very important.