Absolutely no problem with older or newer versions of Office.
An earlier posting said later versions of Office cannot open old documents. Not true. Office 2013 can open documents as old as Office 97 and Works 6, and can save them in those old formats.
That pre-dates OO.org, and for Microsoft if you really need to go farther back than that you can keep an old system running just to convert documents to Office 97 or later.
In the other direction Microsoft has free downloads for Office 2000, XP(2002), and 2003 for Windows and 2004 for Mac that will open OpenXML files created by Office 2007 and later. I have many clients using those and none have had any trouble.
I also know Windows and Linux users who use LIbreOffice. They all use Microsoft default formats because that's what the majority of the world understands.
US Federal and State agencies might specify support for ODF formats, but that doesn't mean they get used, and Microsoft Office supports ODF formats in addition to their own.
