I agree with the advice to speak to an Oncologist, but I'd also suggest talking to another Surgeon, because RT is certainly not a given after surgery on *localised* cancer. Unless you've misunderstood and he was advising that you *might* need it - that is certainly true, just as you might need further action after going the RT route originally.
As noted, after surgery it will take months before you should do things like weigh-lifting, because strain can cause problems with the internal stitching. You're not even allowed to push a supermarket trolley for the first few weeks.
Is it keyhole surgery you are being offered?
As far as incontinence is concerned, I think Chris is offering a gloomy picture - at 62 and fit (presuming that you don't smoke and are not obese) you may have very few continence problems; or you may be unlucky. You have a catheter fitted after surgery and when that comes out you will need to re-train a bit as your "waterworks" will have changed, but that ranges from days to never. You can improve your chances by starting pelvic floor training as soon as possible.