I am so sorry to read about your Dad, he is very lucky to have a daughter like you who clearly loves him very much.
I was diagnosed over 2 years ago, age 49, PSA 342 Gleson 9 spread to lymphs. I want to give you hope that with treatment your dad should have many great years to come. Since diagnosis and chemo, radiotherapy and a few different drugs I am still here, still working, running etc etc. In fact I run more now than I did pre cancer. Last year I ran a 257 kilometre desert race and will do it again this year.
I can remember how hard it was when I was first diagnosed but this forum was so helpful. When I saw the docs I wrote everything he said down, I also had lots of questions from info on this site. The mental battle is harder than the physical one right now.
My PSA is now 0.17 so even when it all kicks off again it will take a while to slow me down.
We are all rooting for you, ask specific questions here if you can but most importantly give your dad hugs often and make him feel loved as that is what he needs from you right now.
Take care, keep posting, believe
Kev