C.R.S. § 24-51-502

(1) A member may qualify earlier for service retirement, reduced service retirement, or increased benefits through the purchase of additional service credit. (2) Service credit purchases are limited to those specified in this part 5. (3) Service credit purchased pursuant to this part 5 by members who were members, inactive members, or retirees on December 31, 2006, shall be subject to the benefit provisions in effect for the existing member contribution account. Service credit purchased pursuant to this part 5 by members who were not members, inactive members, or retirees on December 31, 2006, shall be subject to the benefit provisions in effect for such member at the time of the initiation of payment of the purchase.