The release of Pages v5.5.1 on Yosemite brought with it a means to enable backwards document compatibility with Pages v5.2.2 on Mavericks.
By default, Pages v5.5.1 saves a document as a compressed archive — not a folder. There is no preferences override for this. It is this archive format that is not backwards compatible to Mavericks. However, there is now a File > Advanced > Change File Type menu hierarchy. The two choices are Single File (default archive format), and Package (folder). The first is good for non-Apple filesystems (e.g. Dropbox), and the second, a package folder, is the format that can be opened by Pages v5.2.2 on Mavericks.
When creating a new document, you must first save it before the above menu is enabled. Choosing Package with an open, single file document, will convert it in-place to a package folder within Pages. Recommend you hit File > Save again for good measure.