The phrase "outdated version" refers to something that is old or no longer up-to-date. It means that there is a newer or more recent version available that has improvements or updates. Full definition
For whatever reason Android - based ebook readers always use an older outdated version of Android. (blog.the-ebook-reader.com)
This latter category might include, for example, files created with outdated versions of word processing programs. (discovermagazine.com)
Then there's the fact that phones sold in this segment tend to feature vastly outdated versions of Android with no software updates. (androidcentral.com)