[quote=@Nightrunner]
So I assume Grayson is in his thirties or fourties, Bruce's fifties or sixties, Tim's probably in his thirties, Damian in his twenties?

If Bruce is still running around, an excuse could be a Lazarus Pit.
[/quote]

I always see Bruce as too stubborn to use the Lazarus pit and instead starts to use more Batman Beyond style armors which enhance and support his aging body.