Batman not forever
In the latest Batman comic, Bruce Wayne has been killed off. I haven’t delved deep enough to find out what happens to Batman now, but it may be the start of a line of Batmans, much like the Phantom.
This also begs the question of what would happen when one of the main superheroes grew too old to be of any use. The accelerated growth experienced by Superman as a child would also mean that he would age faster than someone from Earth. Would he fade into oblivion or pass on the torch to one of his offsprings?