I think the liklihood of a minor having to use a firearm in the case of self-defense is much, much lower/smaller than all the other shootings happening or going on because a minor did have easy access to a firearm, etc. So if we are talking about the most amount of lives probably being saved or spared overall here, then it's probably still best to make laws for minors not being allowed to have their own guns or firearms in their possession period, etc. And I recommend the age limit be either 21 or 24 for all guns, but at least 18 federally at least, and states can make their own more strict laws from there maybe. No minor should be able to have their own firearms, or another's firearms that are kept in their possession most of the time mostly, etc, because that should be against the law, etc. But as far as securing them, it's up to the adults how secure they want to make them, etc. If they think they don't need to secure them at all even, then they should still be allowed to choose to not secure them at all even, etc. But if any minor or person underage anywhere ever gets access to their firearms, and something like this is done with them, etc, then they should have to face the full penalties of these new laws, etc, which would be considering them just as much responsible/accountable as the shooter themselves, etc.
But there would have to probably be some laws made so as to define what kind of measures would be considered fully securing a firearm or not, etc, but if people still want to take the risk of not securing them, then let them, etc. But also let them understand the new laws also, and that if something should ever happen with any of their not fully secured firearms under the law, that they will then have to face the full consequences of those new laws also, with very little to no exceptions, etc. Which would be holding them just as much equally accountable/responsible as the shooter or perpetrator themselves, etc.
God Bless.