Yes, you may want a second opinion on the biopsy. If the first report is from Bostwick, I would say you didn't need one, and there are some other well known pathologists (Epstein) that members here suggest. Otherwise, if it is a local or insurance co. directed lab, I would ask for a second opinion. I guess your brother is trusting of his doctors. Remind him when he is up for his first biopsy.
Yes, the doctors suggest what they are comfortable with. My Uro did REQUIRE me to visit with a radiation oncologist before making a decision (the Uro was eventually my surgeon). This is why others are asking whether the "inoperable" statement comes from a GP or Uro/surgeon.
Yes, there are healing intervals in treatment steps. After the biopsy, they have to wait for the perforations to heal before surgery or radiation. My wait was about 6 weeks between biopsy and surgery, then minimum 18 weeks between surgery and radiation. Then you may have normal scheduling / equipment / doctor lead times added on.
From implanting gold seeds or Calypso markers, if they use them, you will need several weeks for the area to heal, and let the markers get stable. Then they would do a planning scan, and you will see another week wait for the doctors to build the plan. See my signature for my "journey". My IGRT was 39 sessions (adjuvant), while the 45 is for primary treatment.
And last for now, yes, age is a consideration. I was told by my surgeon that my age was important, that at 70+ they use radiation more than surgery - expecting that the cure may be worse than the disease. At my RT clinic, there were a number of much older men doing RT as a first line treatment.