(3) The director and agents so appointed shall be citizens of the United States and of the State of Mississippi, and of good moral character. The agents shall be not less than twenty-one (21) years of age at the time of such appointment. In addition thereto, those appointed shall have satisfactorily completed at least two (2) years of college studies. However, two (2) years of satisfactory service as a law enforcement officer and the completion of the prescribed course of study at a school operated by the Bureau of Narcotics and Dangerous Drugs, United States Justice Department, shall satisfy one (1) year of such college studies, and four (4) years of satisfactory service as a law enforcement officer and the completion of the prescribed course of study at such federal bureau school as stated heretofore shall fully satisfy the two (2) years of college requirement. During the period of the first twelve (12) months after appointment, any agent of the bureau shall be subject to dismissal at the will of the director. After twelve (12) months' service, no agent of the bureau shall be subject to dismissal or otherwise have their salary adversely affected except for cause, and any such action against an agent shall be subject to and proceed under the laws, rules and regulations of the State Personnel Board.