Is it better to fly to Prague, rent a car and drive to Munich and leave it or the reverse? Do you have any other suggestions? The driver is age 84 and in good health if that makes a difference.
Why does driver want to drive between Prague and Munich? They have trains. If for some reasons driving is necessary then I would recommend to contact rental company (you can google them) and make sure they would rent to 84 year old.
Is this person alone? Train. Renting a car will involve drop off fees, plus the angst of navigating Prague and Munich. Much more likely to arrive in a good frame of mind on the train!