depending on the kid 5-6 is a good age to teach them to shoot (some kids never seem to mature enough).
I never do the "don't touch" thing. its more of a "not by yourself, ask me to show you" and then allow them to touch, explain how it works, etc. give them all the info you can as soon as they show interest, take it as far as you can (until it's obvious they aren't listening).
IMO if they know they can gave (more or less) complete access, then there is no big mystery to tempt them into getting their hands on it when you aren't around.
most of the exact time and way to approach it depends on your kid, you're the only one who can really judge that. most kids have an automatic curiosity, when it pops up, feed it immediately, otherwise they may go looking for (wrong) info on their own.
as far as the wifes issues. she said no, I bought them anyway, she got over it.