I don't want to seem rude but topics like these are dumb because like others have said Bruce Wayne will always be Batman, just like how Clark Kent will always be Superman and Diana will always be Wonder Woman. They'll be times when they're out of commission(injury, "death" etc) for a couple of years(our time) but it won't last because they'll always come back. These alternate futures like we see with Connor as Superman(pre-Flashpoint) and Damian as Batman will never fully be seen.
If they feel like these characters are getting old, they'll just relaunch or reboot or find a way to make them younger. With the relaunch last year and now making them so young, they won't have to worry about this for a long time.
Nonetheless only Dick Grayson deserves to hold the mantle after Bruce.