yWorks offers only the most recent version of yEd for download.
However, with very few (erroneous) exceptions, yEd is always able to open GraphML files written by earlier versions.
That said, what exactly does happen when you try to open your old file in the most recent version of yEd (3.17.2 as of this writing)?
Could you upload your file here for inspection? (Please do so only if the file does not contain any sensitive data.) Please see How to upload files to yEd Q&A? for instructions on uploading files.