It does seem to be the standard medical practice (at least in UK under the NHS) to insist on many months of HT, before and after RT, irrespective of the man's existing level of testosterone (and without usually bothering even to measure it).
This is meant to ensure 'castrate' level, rather than low level, testosterone.
However, logically, an older man whose libido and sexual functioning has disappeared (naturally) must have far less testosterone than a sexually active man of any age. It follows that any prostate cancer he may have - perhaps it started when he was younger - is getting very little testosterone to 'feed' it. (Even if not quite as little as 'castrate' level.) Therefore, he shouldn't need more than a few weeks of HT, if that.
Unless of course (a) it's just simpler to stick everyone on prolonged HT anyway; (b) the hospital's attitude may be, you'll have prolonged HT before any RT because "that's what we do".
I gather studies have shown that reducing testosterone to castrate level makes RT more effective than leaving men with average testosterone levels. I'm not aware of any studies which show just how much of that benefit accrues from getting testosterone below low-libido levels, and down to sore-nipple hot-flush levels. But other contributors to this forum may have more information.