A Zoning Board of Adjustment is hereby established consisting of seven members who shall be residents of this Borough and who shall not hold any elective office or position under this Borough, each to be appointed by the Mayor of the Borough with the advice and consent of Council, to serve for a term of four years each, except that upon adoption of this chapter, the members of the Board of Adjustment then holding office shall continue therein until their present terms expire, with each succeeding member serving for four years. The terms of any members first appointed under this chapter shall be so determined that to the greatest practicable extent the expiration of such terms shall be distributed evenly over the first four years after their appointment.