(a) Except as otherwise provided by this section and Section 862.0021, each person who performs emergency services or, subject to Section 862.0025, support services as a volunteer or employee of a participating department, regardless of whether the person receives compensation from the participating department for the services, is a member of the pension system.
(b) A person is not a member of the pension system if the person:
(1) is less than 18 years of age;
(2) is subject to a waiting period under Section 862.0021 for which the governing body of the political subdivision is not making contributions during the waiting period;
(3) does not receive a certification of physical fitness or assignment to perform support services under Section 862.003; or
(4) is a retiree, regardless of whether the person continues to perform emergency or support services for a department.