Mo. Rev. Stat. § 41.050
The militia of the state shall include all able-bodied citizens and all other able-bodied residents, who, in the case of the unorganized militia and the Missouri state defense force, shall be more than seventeen years of age and not more than sixty-four, and such other persons as may upon their own application be enrolled or commissioned therein, and who, in the case of the organized militia, shall be within the age limits and possess the physical and mental qualifications prescribed by law or regulations for the reserve components of the Armed Forces of the United States, except that this section shall not be construed to require militia service of any persons specifically exempted by the laws of the United States or the state of Missouri. The maximum age requirement may be waived by the adjutant general on a case-by-case basis.
§ 41.050, RSMo