By your assertion, criminals can keep all the guns they want, without a care. Mentally ill and disturbed people can have guns. 5 year olds can walk into school with loaded guns and be fine.
The founding father's never meant such a thing. What they meant was that, im case of being attacked by a foreign nation, our fighting force should have weapons at the ready.
Personally, I think the SCOTUS misinterpreted the 2nd Amendment to be individuals, when the intent was that a State militia and armory would be available as a check on a federal army. It was never intended as a carte blanc capacity for anyone to become their own warlord.
You are simply ignorant, as usual, if what the founding fathers would do.
The founding fathers understood the most pressing danger to citizens wasn’t from foreign governments, but from our own government officials abusing their positions of power, attempting to control their lives.
That is why the amendments, including the 2nd, are specifically designed to limit the authority and power of government, plain and simple, cut and dry.
Back to the OP, there are some things that might gain enough support to pass congress and not violate the 2nd, which should be the goal.
I think limiting the types of firearms 18-20 year olds can own to bolt action rifles, shotguns, and revolvers (i.e. no semi auto rifles with high capacity mags) as well as any records of minors concerning mental illness or violence should be available to the FBI background investigations when they become adults would be reasonable, could pass congress, and withstand legal challenges.
peace to you