The PowerBuilder license for a new version does not invalidate prior versions. You can run as many different versions as you want on one machine.
The 'super old' part of your information has nothing to do with the license, it has to do with whether the version of PowerBuilder is compatible with the version of Windows you are running and the database interface you are connecting to.
Where I work we are running a PowerBuilder 9 application on Windows 8.1 connecting to Sybase ASE. We haven't had any issues with it.