You are right but there are firefighter academies that take recruits in and if they pass the initial tests and training successfully they are put on a list for openings.It takes years to be a full time firefighter. Most firehouses you have to be a volunteer for like 5 years before you can even be considered. They don't just take some little fuckboy fresh outta high school with zero life experience.
This is my general observation and perhaps other members here who are firefighters might chime in.