The officials preparing jury lists shall select only residents of and qualified and registered electors of the county in which such city is situated; and in making such selection they shall take the names of such only as are not exempt from serving on juries, by the provisions of this act, who are in possession of their natural faculties, and are not infirm or decrepit, of good character, of approved integrity, of sound judgment, and well informed in and conversant with the English language, and free from all legal exceptions: Provided, That the name of any person more than 70 years of age who is otherwise eligible may be placed on a list, but such a person if drawn as a juror shall be excused upon his request, and the fact that such person is more than 70 years of age shall not be ground for challenge for cause.