You would expect the governing Princes of New Jersey or California to set standards that would be suitable and not change them over time to become onerous and restrictive? A law writ today can be changed tomorrow. Camel's noses, tent flaps, that sort of thing.
I agree that the urbanization of the country has diminished the numbers of fathers, uncles, and older brothers who could take a kid "shootin'," with the attendant instruction. But I don't think formalizing it on a legal basis is the way to go.
Used to be the BSA had Riflery merit badges, but I believe that program has been seriously curtailed, if not eliminated.
One solution to the training problem, though, would be universal military conscription. But yeah, try to get away with proposing that nowadays, especially considering the Leftist efforts to reduce the voting age to infancy.
Terry