Knowing that, why take the risk of getting discriminated against because of age? Remember that every department is different, yet similar. Some departments tend to prefer hiring younger folks that have minimal or no experience so they can train them the way they want to and so they can come with no preconceived notions of firefighting. This helps eliminate the "when I worked for Acme Fire Department, we did it this way" comments that we just love to hear. Some departments tend to prefer hiring older folks that have some life experience and maybe even some firefighting experience. This helps eliminate the babysitting and hand-holding that sometimes occurs with the younger folks that have lived at home their whole lives and had their parents wait on them hand and foot. Additionally, some departments prefer hiring older folks because they will probably stay with that department for their entire career, and also appreciate the job more because they have already had the opportunity to bust their rear at a real job.
And then there are most departments that do not really care about the age of the candidates they hire. I have heard of some departments that have had recruits in the academy as young as 18 years old and as seasoned as 50 years old. That proves that age doesn't matter. What does matter is that you are able to pass ALL of the phases of the hiring process and successfully transition yourself into the fire department that takes a chance on you to become a productive and capable member of the fire service.