In addition to the provisions of subchapter I of this chapter, an employee shall be eligible for the early retirement option provided by this chapter beginning with the month after the employee has terminated employment, if:
(1) The employee has 15 years of credited service under this chapter as of June 30, 1991, exclusive of service credited under § 5501(e)(4), (5) and (12) of this title, and shall have attained age 50 on or before June 30, 1991; or
(2) The employee has 25 years of credited service under this chapter as of June 30, 1991, exclusive of service credited under § 5501(e)(4), (5) and (12) of this title, regardless of age.