If any officer or employee of the county or of any district not previously included within the field of membership in the system is brought within the field of membership subsequent to the date upon which the system originally became operative in the county, he shall not receive credit for service or for prior service unless he elects to pay and does pay into the fund within one year after such inclusion, and before an application for retirement is filed, an amount equal to the contributions he would have made had he been a member from the date of his entry into the service of the county or district, together with interest thereon at the rate fixed by the board pursuant to
Section 32033. If during any part of the period for which prior service credit is claimed the rate of contribution was fixed upon the basis of the member’s age at entry into the system, the rate of contribution shall be the rate applicable to the member upon the date of his entry into the system.