I don't have a problem with restricting purchases to those 18 or older. I wouldn't mind not worrying about whether my kids were buying weapons - back when they were under 18.
I don't have that much of a problem with restricting purchases so that violent criminals can't walk into Gander Mountain and buy something. Probably using a felony convinction is too broad. On the other hand there are some violent misdemeanors that we might think about. But it's close enough.
I don't mind needing a license to own a fully automatic weapon.
I'm a little concerned about the move towards getting people's medical histories on line and winnowing out those with severe violent psychological problems. I wouldn't want it to evolve to where the government has a small army of LPCs, psychologists etc. who look deeply into your eyes and decide if you are worthy to exercise a fundamental right.