Yosemite requires Pages '09 v4.3.
If your Pages '09 was originally installed from DVD, and you tried to reinstall it/copy it from a backup drive/Time Machine, it won't work. It must be reinstalled from the iWork '09 DVD (due to dependent system libraries) and immediately thereafter, you must apply the Apple iWork 9.3 update. I would follow that with a Disk Utility verify/repair permissions on your boot drive. Then, reboot. Now, unless you have some other problem that is affecting Pages '09, it should launch like a affection starved puppy.
On the otherhand, if your copy of Pages '09 on your backup medium was obtained from the OS X App Store, and you did not update it before October 2013, it may be a version too old for Yosemite, and with no way to update it now. Using the preceding iWork 9.3 update on an OS X App Store version of Pages will upgrade to Pages '09 v4.3, and no dependent system libraries, so it just dies in place. Don't go there.
Pages documents do not store the version of Pages that created/edited them. A double-click of a Pages document icon on Yosemite, will always open it in the version of Pages located in the /Applications folder, which will be Pages v5, if installed. Missing index.xml dialogs are the attempt to open a Pages v5 document in Pages '09.