The militia of the United States consists of all able-bodied males at least 17 years of age and, except as provided in section 313 of title 32, under 45 years of age who are, or who have made a declaration of intention to become, citizens of the United States and of female citizens of the United States who are members of the National Guard.The Second Amendment is about Militias.
Now, I was in a Militia once (The Illinois National Guard). It was very "Well Regulated". I underwent a background check. I was given a test to determine my mental acuity. I was fingerprinted (because my MOS required a security clearance). I was part of an established chain of command. And despite that, my access to the guns was very regulated. They kept them in a locked arms vault when I wasn't training with them. We were only issued live Ammo when we were on a range, and every round had to be accounted for. .