Any member shall be eligible for retirement if he has:
(1) Twenty-five years or more of service, at any age.
(2) Twelve years or more of service, at age fifty-five or thereafter.
(3) Twenty years of service credit at any age, exclusive of military service and unused annual and sick leave, but any person retiring under this Paragraph shall have his benefit, inclusive of military service credit and allowable unused annual and sick leave, actuarially reduced from the earliest age that he would normally become eligible for a regular retirement benefit under Paragraphs (1) and (2) of this Section if he had continued in service to that age. Any employee who elects to retire under the provisions of this Paragraph shall not be eligible to participate in the Back-Deferred Retirement Option Program provided by R.S. 11:1312.1 or the Initial Benefit Option provided by R.S. 11:1307(E).