So the MC still has his hero powers. Can only one person have them at a time? If so, I can see this being a cause for conflict with the new "hero" later.
New hero also has them... I think. They both made it sound like MC's performance has dropped due to middle age, and that is why he's being fired. Doesn't seem like a good idea to me, but what do I know? Isn't two heroes better than one as long as you can afford both? Dispatch them to different jobs if they can't work together, it's still better for the kingdom. It'd be a different story if there were a third hero to take his place. You'd want to hire the best heroes you can for the lowest cost. IRL workers are fired surreptitiously just for being old (irrespective of performance).