(a) An employee who separates from service, except by removal for cause or charges of delinquency or misconduct, is entitled to an annuity—

(1) After completing 25 years of service as an air traffic controller; or

(2) After becoming age 50 and completing 20 years of service as an air traffic controller.

(b) An annuity payable under paragraph (a) of this section commences on the first day of the month following separation.