(1) Any member with five years of creditable service who has attained age sixty and any original member who has attained age sixty may retire on written application to the director, setting forth at what time the member desires to be retired: PROVIDED, That in the national interest, during time of war engaged in by the United States, the director may extend beyond age sixty, subject to the provisions of subsection (2) of this section, the age at which any member may be eligible to retire.
(2) Any member who has completed thirty years of service may retire on written application to the director setting forth at what time the member desires to be retired, subject to war measures.
(3) Any member who has completed twenty-five years of service and attained age fifty-five may retire on written application to the director setting forth at what time the member desires to be retired, subject to war measures.
(4) Any individual who is eligible to retire pursuant to subsections (1) through (3) of this section shall be allowed to retire while on any authorized leave of absence not in excess of one hundred and twenty days.