A member's benefit shall be one hundred percent vested and nonforfeitable upon the first of the following to occur:
(1) The member's attainment of age fifty-five, the normal retirement age; or
(2) The member's completion of twenty years of creditable service regardless of age; or
(3) The termination of the plan established pursuant to sections 86.200 to 86.366, to the extent the plan is funded.