When a future entrant who attains age 50 or more in service, having 10 or more years of service, withdraws, his age and service annuity shall be fixed as of his age at withdrawal. He is entitled to annuity, after withdrawal, of the amount provided from the following sums on the date of withdrawal:
(1) If service is 20 or more years, the entire sum accumulated for age and service annuity from employee contributions and contributions by the city; or(2) If service is 10 or more but less than 20 years, the sum accumulated for age and service annuity from employee contributions, plus 1/10 of the sum accumulated for such purpose from contributions by the city, for each completed year of service after the first 10 years.