Mich. Comp. Laws § 32.49a
The normal age for retirement of officers, warrant officers and enlisted men shall be age 64. Whenever, however, by reason of any federal law, or rule or regulation made pursuant to such law, and applicable to the national guard of Michigan, any officer thereof, including also the adjutant general, shall be determined to be ineligible for further federal recognition as an officer in his then rank or grade or next higher rank or grade by reason of his age, and his commission in the national guard of the United States is terminated, such officer may be placed on the retired list of officers of the Michigan national guard under the same conditions and with like effect as prescribed in section 35 of this act.
Any officer of the Michigan national guard, including also the adjutant general, who, by reason of physical disqualification for further commissioned service, shall have his federal recognition withdrawn and his commission in the national guard of the United States terminated, may be placed on the retired list of officers of the Michigan national guard, under the same conditions and with like effect as prescribed in section 35 of this act.
In the event of any change of physical condition or by reason of any change of federal law, rule or regulation, any such officer so retired shall thereafter again become eligible for a commission in the national guard of Michigan and for federal recognition as such, and shall be again commissioned in the Michigan national guard, his name shall be removed from such retired list without prejudice to him: Provided, however, That any officer of the Michigan national guard, either active or retired, being found or becoming eligible for a commission in the same or higher rank in the Michigan national guard or the national guard of the United States, who, without good cause, declines to accept such commission when tendered to him, shall not thereafter be placed, or retained, on the list of retired officers of the Michigan national guard.
MCL 32.49a