D.C. Code § 49-401: Militia; persons to be enrolled.

Every able-bodied male citizen resident within the District of Columbia, of the age of 18 years and under the age of 45 years, excepting persons exempted by § 49-402, and idiots, lunatics, common drunkards, vagabonds, paupers, and persons convicted of any infamous crime, shall be enrolled in the militia. Persons so convicted after enrollment shall forthwith be disenrolled; and in all cases of doubt respecting the age of a person enrolled, the burden of proof shall be upon him.