It does sound an aggressive treatment, but the cancer is almost incurable.
All the following ages, time spans and probabilities I quote are rough averages and guesses based on reading posts on here and life experience.
His life expectancy without cancer would be about 87, from 85 onwards QoL is on a rapid decline.
If he had no treatment, cancer symptoms would probably be very unpleasant in a couple of years and probably death at the age of 80.
With the aggressive treatment proposed, QoL during treatment would be OK. I had HT/RT at the age of 53, no big problem. Of course adding in chemo and being 77 might make it a bit tougher. By the age of 80 he would be through treatment and either cured (probably 65%) or the cancer knocked back in its progress by about five years. Either way he will probably have a reasonable QoL from now to 85.
I think no chemo and two year HT are plausible alternatives. QoL during treatment will be a little higher, slightly less chance of osteoporosis from HT. Less chance of cure (probably 50%) if not cured cancer progression probably knocked back two years.
Remember I'm not a medic, everyone's cancer is different and everyone's life is different. I wouldn't want you arguing with an oncologist saying "well some bloke on the internet says we have a 50% chance if... blah, blah ..."
All the above is just to give you an idea of time scales, which years does he want best QoL? How does he want to die (immortality is not on the table)?