[KrisKrinkle]

And let's not forget the militia.

10 U.S. Code § 246 - Militia: composition and classes (emphasis added):

(a) The militia of the Uni ted 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.
(b) The classes of the militia are—
(1) the organized militia, which consists of the National Guard and the Naval Militia; and
(2) the unorganized militia, which consists of the members of the militia who are not members of the National Guard or the Naval Militia.

We'll need to raise that "17 years of age". If you can't buy yourself a gun you shouldn't be in the militia.

[mass55th]

I find it interesting that you can join the military at age 17, and be given a weapon and training, but at 17 you can’t join a police force. Different states have different age requirements for becoming a police/peace officer.