Mo. Rev. Stat. § 86.550
On and after the effective date of sections 86.510 to 86.577 no member of the police department thereafter appointed who is over the age of thirty-five years, that is, who has attained his thirty-sixth birthday, and who is unable to pass a physical examination by a physician designated by the board of trustees of the police pension fund, shall be eligible to become a member of such fund, except persons who had theretofore served not less than four years in said department, the last service being not more than five years before their reappointment to the department. If a member of the police department is appointed by the board of police commissioners, who is over thirty-five years of age, that is, has attained his thirty-sixth birthday, or is unable to pass a physical examination provided by sections 86.510 to 86.577, such member shall not be permitted to become a member of the police pension fund, nor shall he be liable for any assessments for the support of such fund; provided, that nothing in this section shall be construed to apply to the reappointment of any member of such force at the expiration of his term of appointment in such department.
§ 86.550, RSMo