Tenn. Code § 8-3501
After July 1, 1949 and before the time specified in § 8-3452, any member of the retirement system in the employ of the state or whose employment has ceased within the sixty (60) days immediately past, may begin participation in benefits hereunder, upon giving the board thirty (30) days' written notice, provided he has attained sixty (60) years of age, has rendered an aggregate of twenty (20) years of current service and certified prior services to the state of Tennessee, or, if he is a commissioned member of the department of safety, provided he has attained fifty (50) years of age and has rendered an aggregate of twenty-five (25) years of service, or, if he is a fireman or policeman employed by a political subdivision covered under the Tennessee state retirement system, provided he has attained fifty-five (55) years of age and has rendered an aggregate of twenty-five (25) years of creditable service, or, if he is a commissioned member of the enforcement and field services division of the game and fish commission, provided he has attained fifty-five (55) years of age and has rendered an aggregate of twenty-five (25) years of creditable service, and has complied with all other requirements for participation in benefits of this retirement system; or, after July 1, 1949 and before the time specified in § 8-3452, any member in the employ of the state, or whose employment has ceased within the sixty (60) days immediate past, may begin participation in the benefits of the system, upon giving the board thirty (30) days' written notice of his desire to participate, provided such member has a total of thirty (30) years of current service and certified prior service to the state of Tennessee, and has complied with all other requirements for participation in benefits of the system.
Any member may retire on a service retirement allowance, upon giving the board not less than thirty (30) nor more than ninety (90) days' written notice thereof, provided the member shall have attained the minimum retirement age for his class as provided below:
However, any fireman or policeman employed by a political subdivision covered under the Tennessee state retirement system and any commissioned members of the enforcement and field services division of the game and fish commission shall have attained fifty-five (55) years of age and have an aggregate of twenty-five (25) years of creditable service.
T.C.A. § 8-3501