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My buddy always used to say, "you plant potatoes, you get potatoes'. You get in your children what you "plant". If the kid seems immature, or lacks character, then look to the mirror for the source. Its not the kids fault they had faulty programming.
You are mistaken.
I have 4 children, each of whom is AND HAS BEEN FROM BIRTH a unique individual with his/her own distinctive characteristics -- including his/her distinctive rate of maturity gain. Parents have some influence, but inborn temperament is a major influence on their development.
My oldest son has always been amazingly responsible and mature for his age. Being in addition large and strong, as a 3yo he was mistaken for a kindergartener, as a 14yo he passed for an adult in our Civil War Reenactment group (the captain said he trusted our son with the guns more than he trusted some of the middle-aged guys), and as a 17yo he was taken for the father of his two younger brothers, then 3 and 8. Had it been legal I'd have trusted him to carry from the time he was 16. Had we stopped at one child I might have agreed with you that parents could create responsibility if they tried.
My daughter was a difficult child to raise because she was a rules-tester and completely lacked a sense of personal danger. I had to cling tightly to her hand in parking lots until she was 6 or 7 because she just didn't understand that moving cars could hurt her. Had we been shooting at that time we'd not have dared take her to the range unless we were prepared to keep a hand on her at all times. It was not that she intended to misbehave, but there was something in the way she was wired that didn't let her envision the possibility that the world could hurt her. Then she hit puberty and matured in a tremendous rush. She developed at least a modest sense of self-preservation and became highly concerned about danger to others. She's even taken the Range Safety Officer course and, though not old enough for certification, is often our family's range officer due to her superior situational awareness.
My 11yo is a highly compliant child who does what he is told -- IF he listens. His head is in the clouds most of the time and he's prone to "good ideas". He means well and wants to make us proud, but he has very little common sense. When he's at the range with us he requires tight supervision, not because he doesn't want to obey the rules and do well but because he loses focus. When shooting we keep him the line between 2 of the adults so we can keep him tracked on what he is doing.
The 6yo is more contrary than the others -- a rules-tester like his sister, but is developing a good deal more sense than the 11yo. The only time he's been shooting he handled the Crickett well, even learning to load and cock it himself. At that age he, of course, requires an adult to give up shooting and devote the session entirely to monitoring him. But his responsibility level is high unless he's in a contrary mood.
Any mother who has borne several children will be able to confirm that you can tell a lot about your kids while you're still pregnant. You learn their activity level, their intensity level, and something about their up/down patterns. You can can bend the twig to some extent, but much about its nature is set by nature and you get far better results by working with a child's nature than against it. But there is no guarantee that you'll get the results you want at all.