I'm 3 years after prostatectomy, which left me with 50% of the nerves. Before surgery I'd do up to 45 miles on mountain bike (Hertfordshire) twice a week which i thought was reasonably active at 60 and cycle 10 miles round trip to station and back each day.
I had a lot of perineal discomfort after surgery. I did keep walking got up to 3-5 miles a day 3-4 months after surgery and have kept that up. Tried cycling after 9 months and it was OK but would usually be uncomfortable afterwards, not too bad but some pain that would move around, balls, perineum, penis. Surgeon did say it was scar tissue and it was OK to challenge myself, but I stopped after I slipped whilst walking which left me sore for a couple of weeks. Next summer tried again same thing, it was some discomfort but I overdid it carrying stuff so I stopped
This year i restarted after winter, as usual feeling a bit uncomfortable after ride. My surgeon said push through it may break up scar tissue which I did and have persevered and now riding twice a week and now any post-ride discomfort pretty much gone (so far). I'm not up to the same distances but building up, and now in Torquay so every ride involves up and down the steep sided valleys between Torquay and Teign Valley, there's a lot more climbing than around Watford - St Albans. I do roads and the gentler off-roads. Many tracks are also by-ways and are challenging enough on a Honda CRF250.
I do use saddle with cut out and have played around with stems, bars and saddle position to get comfortable riding position, being too stretched out wasn't good. I think getting position right was important