How can I open a Pages file prepared with Yosemite in OS X 10.8.5?
If the originator of the file can share it with you using iCloud, you can open it on any web browser via the link.  You will there be able to edit the file.

If you want to edit the file in older versions of Pages, download the file as a Word (I know, right!) document then open that in your version of Pages.  Some formatting my be lost, but you can at least now work with the file locally.

Conversely, your colleague could send you the file already as a Word document for you to open in Pages for editing.