it will be more to do with fitness levels than his age. Mr CRX is retained but i doubt he'd pass medical for full time at the moment.
My sister in law has just become a full time firefighter at 44 but then she puts most people to shame fitness wise lol
Get him to contact his local fire station and ask for their advice.
Perhaps whilst he waits for any full time placements he could look at becoming a retained firefighter if they have them.
Be warned though, retained means he would be on call 24/7 365 days a year and cant stray far from the area. Its very restrictive, but if he is determined that its the career for him then it would be a good starting point.