(a) Requirements; all candidates. Except as otherwise provided in this section every candidate for examination for appointment in the grade of assistant:

(1) Shall meet the requirements for eligibility for examination for appointment in the grade of junior assistant;

(2) Shall be at least 21 years of age; and

(3) Shall have had at least 7 years of educational and professional training or experience subsequent to high school, except that a candidate who applies for examination for appointment in the Reserve Corps to serve as a medical or dental intern may be examined for such appointment upon the completion of 6 years of such education, training, or experience.

(b) Additional requirements; dietitians. Every candidate for examination for appointment as a dietitian shall have successfully completed an approved training course for dietetic interns.