Commissioned officers and warrant officers shall be citizens of the United States and shall be at least twenty-one years of age or such lower age as may be authorized for appointment as reserve officers of the army or the air force by federal laws and regulations. They shall be appointed upon the order of the governor, subject to federal recognition as commissioned officers and warrant officers in the army or air national guard, except as to those officers appointed as aides-de-camp to the governor and staff positions not requiring federal recognition. Officers and warrant officers whose appointments are subject to federal recognition shall meet the qualifications prescribed by the secretary of the army or the air force, as the case may be. The commissions of all officers and appointments of warrant officers shall continue in force indefinitely and until they are separated from the service of the national guard in accordance with this chapter.