iOS 9 should work on any iPad except the original iPad 1. If your iPad has a camera, it should work.
I think you might not have enough free space on the iPad to decompress the update. What version of iOS is on there now?
Try freeing up space on the iPad. If that doesn't work, make a backup of it in iTunes then clear all content and settings and then try it. Last resort would be DFU mode and restore.
Source:
http://ift.tt/1O6DAXi