If mandatory training really is important, including optional firearms safety classes during high school might be worth a try. That way when the student becomes old enough to purchase a firearm he will already of had training.
I second this. If kids already get information about driving safety and regulations at school, it wouldn't be a bad idea that they get the same about firearms, but you'll have to deal with anti-gun parents, then.
IMHO, some training is needed to handle firearms and it makes sense to make it mandatory.