Some jobs have extra medical requirements after a certain age. If you pass them you are fine no matter your age. Some jobs you are retired at a certain age. What do you think?
In Ireland you are automatically retired as a firefighter at 55. Here is Mike Tyson training at 55. I would think he would be fit to be a firefighter at his age and better than most men in their 20s. https://www.youtube.com/watch?v=KQmSonaNUwk