Section 20. A person shall not be eligible for appointment or to be appointed as an officer in the armed forces of the commonwealth if the individual is: (i) not a citizen of the United States and 18 years of age or over; (ii) under sentence of a court or board which disables such person from holding office or command; (iii) under suspension from command in the armed forces of the United States or of any state; (iv) under sentence of imprisonment by a civilian court, whether suspended or not; or (v) ineligible for such service under the laws of the United States. No person shall receive a commission in the national guard, army or air unless such person possesses such minimum qualifications as prescribed by the laws of the United States and has qualified for such commission.