Here’s an idea I had, maybe it’s too restrictive, maybe not, but here’s a basic concept to handle the “well regulated” part of the 2nd amendment:

Hunting weapons/Light rifles and shotguns - No change to requirements. Relatively easy to obtain. Safety course required. Background check required.

Handguns/> - Must be at least 21. Safety course and background check required.

Assault rifles and heavy weapons - Must be at least 21. Safety course and waiting period required. Certain exemptions for service members/law enforcement/etc. Background check required.

Gun ranges are permitted to carry a variety of weaponry on site including assault rifles for those who wish to “try before they buy” and/or train with such weapons in a safe, controlled environment.

You’ll notice this approach does not ban or outright prohibit any weapons whatsoever.