A member who has acquired a vested right to a retirement annuity as set forth in section 15-39.1-11 and who has attained age fifty-five may retire prior to the normal retirement age as set forth in section 15-39.1-10 but the benefits to which the member is then entitled must be reduced according to the following schedule:

1. All tier one grandfathered member benefits must be reduced by six percent per annum from the earlier of: a. Age sixty-five; or

b. The age at which the sum of the member's current years of service credit and years of age equals eighty-five.

2. All tier one nongrandfathered member and tier two member benefits must be reduced by eight percent per annum from the earlier of: a. Age sixty-five; or b. The later of: (1) Age sixty; or (2) The age at which the sum of the member's current years of service credit and years of age equals ninety.