Yep, super old thread. I didn't look through it but I'll reply anyhow. Heck, I may have replied already.
I started taking my kids out with me at about age 5 I believe, teaching them what hunting was about. Short hunts in nice weather. They learned to enjoy going and looked forward to it each season. My son shot his first deer (a doe) at age 8 or 9, can't remember exactly now. My daughter at age 12 (she wasn't ready earlier). I think its great to get them involved early. One thing to consider - all kids levels of maturity vary...some 12yr olds aren't as mature as some 10yr olds, etc.
I know some states do have min age laws, and imo, if they feel they have to have them, it shouldn't be older than 12. Some states you have to be 15 to hunt which is ridiculous to me. My son had shot a dozen deer and was hunting on his own by 15. He was a more seasoned, safe, and mature hunter than some of the adults I know. He was also more interested in girls by then, than hunting. If I couldn't have taken him since he was little who knows if he'd even have gotten into hunting.