Before Batman v. Superman: Dawn of Justice came out, I assumed the casting of an older actor in the role meant that he had been Batman for a bit, retired, and the rise of Superman caused him to come out of retirement.
However, in the film it's implied he's only been active for a while; the fact he's not called Batman but "the Bat" (IIRC) and from conversations between Perry White and Clark Kent.
Is there an in-universe or Word of God statement as to how long Bats has been going about his business?