Thought on National Guard and the militia
10 U.S. Code sec. 311 gives the legal definition of the federal militia.
(a) says the militia of the US consists of all able-bodied male citizens (or who have declared their intent to become citizens), age 17-45, and of female citizens who are member of the National Guard.
(b) says the classes of the militia are the organized militia, the National Guard and Naval Militia, and the unorganized militia, which is all other militia members.
But a bit of research shows retirement age for the Guard is well above 45. In 2005, the Senate approved a measure to lower the retirement age from 50 from 60. Neither of those are mandatory retirement ages, just ones at which (with 20 years' service) it is possible.
It would appear to me that the National Guard thus includes persons who are not members of the "militia of the United States."
Hmm.... and here's an indication that you can enlist in the Guard if you are are permanently admitted to the US and requested permanent residence. I don't know if that requires declaring an intent to become a citizen.