(a) Each member of the board at the time of his appointment and qualification shall be a citizen of the United States and a resident of the Commonwealth of Pennsylvania, shall have been a qualified elector in the Commonwealth for a period of at least one year next preceding his appointment, and shall be not less than twenty-one years of age.

(b) No member of the board during his period of service as such shall hold any other office under the laws of this Commonwealth or of the United States.

(c) Board members shall devote full time to their official duties. No board member shall hold any office or position the duties of which are incompatible with his board duties.