Mich. Comp. Laws § 38.1381

Sec. 81. (1) Except as provided in section 81c, a member who no longer is working as a public school employee or in any other capacity for which service credit performed in this state is allowed under this act, upon the member's written application to the retirement system, shall be entitled to a retirement allowance provided for in section 84 if 1 of the following applies: (a) The member is 55 years of age or older and has 30 or more years of credited service as provided under this act of which at least 15 years were served as a public school employee. (b) The member is 60 years of age or older and has accumulated 10 or more years of credited service as a public school employee. (c) The member is 55 years of age or older and has 15 or more years of credited service, but less than 30 years of credited service of which the last 5 consecutive years are immediately preceding the member's retirement allowance effective date. (2) Except as provided in section 81c, for a member who contributes to the member investment plan, the eligibility requirements of subsection (1) shall be modified as provided in section 43b.