The Constitutional issue is known as "prior restraint" alternatively understood as "guilty until proven innocent" and is specifically prohibited by the Constitution.
History is littered with examples of government arbitrarily and capricously assuming guilt and acting on that presumed guilt with extreme prejudice.
One oft referenced example is, of course, the policies of the duly elected German Government toward various segments of their population such as Jews, Gypsies and other non Aryan people.
The possession of armament by the general population (including military weapons such as shoulder fired missiles and various explosives-grenades,land mines etc.) is intended as a check and a balance on the capability of a Government to wage war on its own population.
Hope this helps.
I agree with that.
I will research "Prior Restraint" but I would think the Founders meant that you must be of, at least, "militia" age. I would also think that being neither crazy nor criminal could be assumed.