while no your son can't play airsoft
this is how ever a great way for you to spend tme with him as nothing says fauther son time like shooting things it's worth well allot
and ignore fox as they're are parents who's kids use real guns like 12 shot guns in they're supervission and have since they where 8. and heck my GF's 7 year old is learning to play
a realy good book on safe handling of guns is the CFSC course manual acts and prove are the most vital part of it and if you wanna teach your kid properly no is the time to do so
the 18+ in general rule is not hard line it depends also on the location as some place's require people to be 18 for insurance reasons though they're are some that allow 16. this 18 and up rule is because even if you hide fun things from kids they instantly become mature and responsible the instant they turn 18... wait can someone say coalition government of irresponsibility they're what 80 years old each and they whine like children cause they're corporate friends aren't gonna get a bail out cause our government is responsible.
think of it this way they're are worse things he could be doing if he show's an interest in firearms and shooting it's never going away use it as away to spend as much time with him while you are still invincible and can do any thing i missed out on that time with my dad and i regret that every single day enjoy it while you can.
also statistically speaking it's a proven fact that kids who shoot thing with they're father's such as target shooting and hunting are 99x less likely to be involved in crime then kids who's parents go "guns are bad"