If you can migrate form version 7 to version 9 then you must be able to compile code. Therefore there is no justification at all for stopping at 9.1D. Are you also upgrading everyone's desktops to Windows 3.1?
9.1D is ancient, obsolete and unsupported. (Just imagine what that makes 7.1E...)
Progress for AIX is 32 bits only prior to 10.0B.
Current releases are 10.2B06 and 11.0.
On the bright side he isn't actually asking you to do it. Just research it as a "test of skills". Hopefully that means that there is no actual 7.1E database nor any plan to do something as ridiculous as implement a 9.1D system in 2012.
Anyhow, if your senior is "testing your skills" the skill that you are exercising is "internet research" so you should pull together all of the issues and comments and probably grab a copy of the "product availability guide" from Progress' website to help document what you have been told here.