Under such rules and regulations as the board of trustees shall adopt, each member, who was a teacher at any time during the five (5) years immediately preceding the establishment of the system and who became a member before July 1, 1950, may file before July 1, 1959 a detailed statement of all service as a teacher rendered by him prior to the date of establishment for which he claims credit.
T.C.A. § 49-1513