Any city which shall have operated for more than six years since the adoption of the city council system of government or since the last election at which the question of changing from the council system was rejected by a vote of the qualified electors, may change its organization thereunder and adopt the city commission form of government. The proceeding to change shall be initiated by a petition asking for such change signed by not less than forty percent of the qualified electors of the city, as determined by the total number of qualified electors voting at the preceding general election. The signatures to such petition need not be appended to a single paper, but one of the signers upon each paper shall make oath before an officer competent to administer oaths that each signature appearing upon such paper is the genuine signature of the person whose name it purports to be. Each petition, in addition to the names of the signers, shall contain the name, address, and age of each petitioner, and the length of the petitioner’s residence in the city. Any petitioner shall be permitted to withdraw that petitioner’s name from a petition within five days after the petition is filed.