Although age is a factor in making treatment decisions - the most important one is the chance of recurrence in YOUR lifetime.
Younger men in their 50’s or 60’s with your aggressive Gleason score may opt for surgery since the chance for recurrence is greater in their longer anticipated lifespans. Because of this, recurrent cancer can then be treated with radiation and/or ADT.
In your case, being 80 years old and in excellent health, you have a good chance of living 10 yrs or more; the 10-15 year outcomes (successes AND failures) for surgery and radiation are the same.
That being said, you may opt for the lesser invasive treatment, which is the 5 fractions of radiation (cyberknife) mentioned by others since you are not looking at a 20+ year lifespan (just being realistic, nothing more)
Also be aware that you may be advised on a short course of ADT to weaken the aggressive cells further. You really need a Decipher Test to show the true aggressiveness of your cancer - Gleason 8 is a measurement of relative amounts of aggressive cells; more of the worse ones!
Decipher is the test to see HOW ‘worse’ they are…if more aggressive, short term ADT may be prescribed.
There is also a ‘boost’ radiation therapy which involves temporarily placing a powerful radiation source inside the prostate itself for about an hour (under sedation). This ‘boost’ called HDR brachytherapy is usually followed by conventional radiation of 4-5 sessions (cyberknife type) or IMRT, 25 or more sessions administered to the prostate and pelvic nodes.
From my post I think you realize that there are many gray areas here; it’s not simply surgery OR radiation.
I suggest you go to a hospital or center with a well known, skilled cancer team. Their radiation oncologists will be able to assess what is best for YOU, since (here it comes, guys) we are ALL different! Best,
Phil