What old version? What operating system? You need to be more specific. That said, things simply move on. Apple and Microsoft change stuff all the time and old programs becoming incompatible with newer versions of OS X or Windows is just a normal thing outside Adobe's control.
If you need an older version of your Adobe application(s) to work with an older Mac, you ought to be able to find a version you can use on one of the following pages here (see at the bottom of the first page),