Sec. 11. RETIREMENT PENSION. From and after the passage of this Act, any member of such Pension System who has been in the service of the city Police Department for a period of twenty-five (25) years shall receive from the Pension Board a pension certificate. Any person who holds a pension certificate and who has attained fifty-five (55) years of age shall be entitled to a monthly retirement pension equal to one half (1/2) of his statutory minimum pay plus one half (1/2) of his longevity pay, which he received when such certificate was awarded, each month for the rest of his life upon his retirement from the services of said city Police Department; provided, however, said monthly retirement pension shall not exceed the sum of One Hundred and Twenty-five Dollars ($125). However, when a member has served twenty-five (25) years or more in the Police Department and has attained the age of fifty-five (55) years, if he desires and if the physicians employed by the Pension Board agree that said member is physically fit to continue his active duties in the Police Department, he may continue such duties until he is not over sixty-five (65) years of age, and when he retires he will receive in addition to his monthly retirement pension set out above, a service bonus of One Dollar ($1) per month for each year of service over and above the amount per month payable if he had retired when he attained the age of fifty-five (55) years. It shall be compulsory for any member to retire from service upon attaining sixty-five (65) years of age; failure of any member of the Pension System to comply with this provision shall deprive the member or his dependents of any of the benefits provided for herein. If at the time of retirement such member has completed less than twenty-five (25) years of service, but more than twenty (20) years of service, his retirement pension shall be prorated. For example, if the employee has completed only twenty (20) years of service, his monthly pension would be four-fifths (4/5) of one half (1/2) of his statutory minimum pay and one half (1/2) his longevity pay. No member shall be required to make any payments into the Pension System Fund after he has been issued a pension certificate and who has retired from active service in the Police Department. However, if he continues to work for the city Police Department after receiving a pension certificate, he shall continue his monthly payments into the Pension System Fund until he retires.