The new versions of Pages, Numbers and Keynote require iOS 10 or later.
If you need a compatible version for iOS 9, you'll need to download the incompatible versions via iTunes on a computer first, so they are associated with your Apple ID, and then follow the steps here to get compatible versions on your iPad.
Install an app on an earlier version of iOS or OS X - Apple Support
You do not need to connect the iPad to the computer at any time. Just download the Apps in iTunes, and then find them in Purchased tab in the App Store App on your iPad.
Note as mentioned this method may stop working once iOS11 iks released.