For the purpose of the Retirement System, any officer or employee of the police or the fire departments whose employment therein began prior to January 1, 1900, or whose employment therein began on or shall begin after that date and was or shall be subject to a Charter maximum age at the time of employment of not over 35 years, shall be considered to be a member of the police department or the fire department, respectively. Any fire or police service outside the limits of the City and County performed by a member of the Retirement System and under orders of a superior officer of any such member, shall be considered as City and County service, and any disability or death incurred therein shall be covered under the provisions of the Retirement System.