You cannot wrap them up in cotton wool,nor watch them every second.You can only tell them,show them,let them try for themselves,ready to step in if something looks like going wrong. Yes,they will get a few cuts and and a few frights,but that,s all part of the learning process.
The amount of instruction I received,even when I worked in a huge machine shop,at 16 years old,could be written on the back of a stamp.My wood machining is self taught,with the aid of a few good books on the subject.
Kids are not as helpless as we might think,they learn fast if they are interested,and if they are not,they have no place in a workshop anyway, Give him a try,you might be surprised. Just explain that machines NEVER SLEEP and need to be treated with respect ALL THE TIME.
He might end up teaching you a thing or two !! Has happened !
Good luck,it,s nice to hear of some young lad showing an interest in such things,most just cannot be bothered.