(a) Any member, whether over or under the minimum age of voluntary service retirement, who leaves county service after completing five years of service or who leaves county service and within 90 days, or six months if Section 31840.4 applies, becomes a member of the Public Employees’ Retirement System, a retirement system established under this chapter in another county, the State Teachers’ Retirement System, or a retirement system of any other public agency of the state that has established reciprocity with the Public Employees’ Retirement System subject to the conditions of Section 31840.2, may elect in writing, within 90 days after establishing eligibility for reciprocity, to leave his or her accumulated contributions in the retirement fund and be granted a deferred retirement allowance to become effective either:

1. (1) Upon the option of the member, at any time at which he or she could have retired had he or she remained in county service in a full-time position.
2. (2) Not later than the first day of the month following that in which he or she attains the applicable compulsory retirement age, if any.