Ipod 4th gen won't allow to update from iOS 6.0.3 and will not allow download Facebook or update and download other apps unless upgraded to iOS 7 or better
Se if a compatible, earlier version is available
Starting when iOS 7 was released, Apple now allows downloading the last compatible version of some apps (iOS 4.2.1 and later only)
App Store: Downloading Older Versions of Apps on iOS - Apple Club
App Store: Install the latest compatible version of an app
You first have to download the non-compatible version on your computer. Then when you try to purchase the version on your iPod you will be offered a compatible version if one exists.
iPod 4 will not update from version 6 thus not allowing download of Facebook and other apps. Warning states needs to update to version 7 or betters
