No person may be popularly elected to and serve in any office in this State or its political subdivisions unless he possesses the qualifications of an elector, is not disqualified by age as prescribed in this Constitution, and has not been convicted of a felony under state or federal law or convicted of tampering with a voting machine, fraudulent registration or voting, bribery at elections, procuring or offering to procure votes by bribery, voting more than once at elections, impersonating a voter, or swearing falsely at elections/taking oath in another's name, or has not pled guilty or nolo contendere to these offenses. However, notwithstanding any other provision of this Constitution, this prohibition does not apply to a person who has been pardoned under state or federal law or to a person who files for public office fifteen years or more after the completion date of service of the sentence, including probation and parole time, nor shall any person, serving in office prior to the ratification of this provision, be required to vacate the office to which he is elected. No person may be elected or appointed to office in this State for life or during good behavior, but the terms of all officers must be for some specified period except officers in the militia.