The militia of the state shall consist of all able-bodied male citizens of the state and all other able-bodied males who have, or shall have, declared their intention to become citizens of the United States, resident within the state, and who shall be more than eighteen (18) years of age and, except as hereinafter provided, not more than forty-five (45) years of age, and such other persons as may upon their own application be enlisted or commissioned therein.