The board of police commissioners shall appoint a chief of police who shall be the chief police administrative and law enforcement officer of such cities. The chief of police shall be chosen by the board solely on the basis of his or her executive and administrative qualifications and his or her demonstrated knowledge of police science and administration with special reference to his or her actual experience in law enforcement leadership and the provisions of section 84.420. At the time of the appointment, the chief shall not be more than sixty years of age, shall have had at least five years’ executive experience in a governmental police agency and shall be certified by a surgeon or physician to be in a good physical condition, and shall be a citizen of the United States and shall either be or become a citizen of the state of Missouri and resident of the city in which he or she is appointed as chief of police. In order to secure and retain the highest type of police leadership within the departments of such cities, the chief shall receive a salary of not less than eighty thousand two hundred eleven dollars, nor more than one hundred eighty-nine thousand seven hundred twenty-six dollars per annum.