No person is eligible to hold the office of judge of probate who is not at the time of his election a citizen of the United States and of this State, has not attained the age of twenty-one years upon his election, has not become a qualified elector of the county in which he is to be a judge, and has not received a four-year bachelor's degree from an accredited post-secondary institution or if he has received no degree he must have four years' experience as an employee in a probate judge's office in this State.