I'm hoppy and at 49 have had pd for about 13 or 14 years. Advice, meds, etc....
First you must love your dad if you are taking the time to find out more. Just always remember he's your dad even when he does strange things or can't hardly get out of bed. I have taken so many meds, Sinimet (carbidopa/levidopa) Mirapex, Tasmar, eldypril, Tocapone, requip, and several more that I don't remember rignt now. Sinimet, IS the gold standard! the others help the sinimet to last or increase the effects of it.
Suggestions, MAKE SURE YOUR DAD is seeing a movements disorder nueorologist. NOT JUST A NUEROLOGIST! There are centers for excellence on other websites, you can find them there. It is the difference between taking you Ferrarri to Joe's fixit shop and the Ferrarri dealer. I used to drive 600 miles to the doctor, she was worth the trip.
His doctor, if he's any good can or should be able to, adjust and know the current meds on the market. If he or she doesn't GO ELSEWHERE. You don't have to feel that all docs are alike, they are NOT. You only get so many years after the diagnosis... I was very lucky to have DBS surgery, and it has gave me a new chance, I'm not 100% but a heck of a lot better than before.
GET A GOOD DOCTOR!