(a) All applicants for a position in the fire department of the fire protection district shall be under 35 years of age and shall be subjected to examination, which shall be public, competitive, and free to all applicants, subject to reasonable limitations as to health, habits, and moral character; provided that the foregoing age limitation shall not apply in the case of any person having previous employment status as a fireman in a regularly constituted fire department of any fire protection district, and further provided that each fireman or fire chief who is a member in good standing in a regularly constituted fire department of any municipality which shall be or shall have subsequently been included within the boundaries of any fire protection district now or hereafter organized shall be given a preference for original appointment in the same class, grade or employment over all other applicants. The examinations shall be practical in their character and shall relate to those matters which will fairly test the persons examined as to their relative capacity to discharge the duties of the positions to which they seek appointment. The examinations shall include tests of physical qualifications and health. No applicant, however, shall be examined concerning his political or religious opinions or affiliations. The examinations shall be conducted by the board of fire commissioners. In any fire protection district that employs full-time firefighters and is subject to a collective bargaining agreement, a person who has not qualified for regular appointment under the provisions of this Section shall not be used as a temporary or permanent substitute for certificated members of a fire district's fire department or for regular appointment as a certificated member of a fire district's fire department unless mutually agreed to by the employee's certified bargaining agent. Such agreement shall be considered a permissive subject of bargaining. Fire protection districts covered by the changes made by Public Act 95-490 that are using non-certificated employees as substitutes immediately prior to June 1, 2008 (the effective date of Public Act 95-490) may, by mutual agreement with the certified bargaining agent, continue the existing practice or a modified practice and that agreement shall be considered a permissive subject of bargaining.