My radiation oncologist had the same attitude toward hormone therapy (ADT), he quoted me that it only gives 3%-5% better outcomes. He also feels that 6mos to 12 mos of the drug is plenty. My surgeon on the other hand is adamant that I be on the drug for 2 years. (I'm at 16 mos at this point)
My feeling was "gimme all ya got doc!" But my RO would have been quite comfortable with my not taking it as well. We have to make those decisions for ourselves.
I was diagnosed at 61 though. Theoretically, I'd have a couple more decades than your friend, (sorry, there's just no nice way to say that). If I was 79, knowing what little I do now, it would depend on my QOL, activity level etc.. as to if I'd take the drug or not.
Its a personal decision all of us in this situation face. "Given my current age, health, other potential issues do I want to put myself through this?"
The side effects seem to be different for different folks, I have hot flashes for the most part. This makes it tough to sleep sometimes. I stay very active to combat the effects. I have a couple other things mentioned in the potential side effects but it might just be from my age and other gifts I got from my father's genes.
The purpose, as I understand it, of the hormone therapy is to weaken the cancer cells by essentially depriving them of their food, testosterone. It is believed that the weakened cells become more susceptible to the damaging radiation which alters the dna of the cell making it impossible for the cells to replicate, instead they just die off. (or at least that's the plan)
I realize this wasn't much help, but, I guess it sometimes helps to read others thought process and experience. Your dear friend is lucky to have you to support him!
Best of luck to both of you going forward!