Hi Eduardo;
Oracle 11G was first officially supported in PB 12.0 era. PB just calls the Oracle client to broker the DBMS interaction. Up to PB 12.5 you can only use the 32bit client. However, in PB 12.6 you can use either the 32 or 64bit clients as PB supports both bitness options.
The relationship between the DB client & server is like a balanced set of tires on your car. You would normally not mix different manufacturers or types as this can cause handling issues. The same consideration can be applied to PB & Oracle.
Now you can use the older Oracle client as others have indicated. You'll have to weight the technical ramifications of running mixed Oracle clients as you probably have other applications that use the proper O11G client while your outdated PB uses the outdated O9i client.
Which ever way you decide to go - the key moving forward will be to very diligent in testing your unique software combination.
Good luck!
HTH
Regards ... Chris