Before the 1.18.0 update, Old was one of three selectable world types alongside Infinite and Flat. With the possibility of having an Old-sized Flat world now becoming improbable, I've decided to make a downloadable world of one for anyone to use!
Select version for changelog:
Changelog
Since the 1.18.0 update, the Old world type has faced severe bugs that broke existing Old worlds. As of the 1.20.1 update, these issues on the bug tracker, namely MCPE-160718, have unfortunately been closed as Won't Fix.
Due to the unlikelihood of Old worlds being fixed, I have converted the Old Flat World to the Flat world type with 256 block layers of Invisible Bedrock.