Not an easy decision at first. I found that the "answer" became clear though.
Diagnosed at 50 with a small volume of Gleason 6 and some family history (father diagnosed late with stage 4 and bone mets). This by MRI and template biopsy.
The diagnosing consultant advised RP but was happy enough to support me going through my own choice process so I saw surgeons and oncologists before making my decision.
None of them liked the idea of AS for me, primarily because of age they said, but also family history. I did challenge this on the grounds that I (being fully functional) had it all to loose. The response to this (from a surgeon, though not the one who ultimately did the op) was that I also had the most to gain with early action giving the best chance of the best result with regard to nerve sparing and minimising the (hopefully small) possibility of spread.
Likewise, RT was not favoured as being young was felt to increase the chance of late side effects. The exception to this was brachytherapy but that was ruled out in my case due to prostate size.
A history of prostate symptoms related to chronic inflammation and large size rather than PCa also influenced my decision as did my somewhat anxious nature which tends to the old surgical saw "the only good carcinoma is the one in the bucket".
At this point, approaching 4 months post op, and despite some untypical post op complications, I'm content with my decision. I'm fully continent, ED is controlled by drugs (nasty hangovers though) and improving and PSA more or less unmeasurable.
Hope this helps a little and I wish you well in your journey