This is a question of control - or lack of same. If you remain/become very active physically, eat right and live a healthy lifestyle you can literally add years to your life.
A recent study (longitudinal over 20 years) found that persons who got at least 2 & 1/2 hours a week of aerobic outdoor exercise (fast walk, run, jog, bike etc) plus at least 2 weight training sessions (load bearing exercise) a week had a 26% lower chance of dying from all causes and a 31% lower chance of dying from cancer compared to non-participants. There are several other studies that report similar results.
Additionally, there are a number of supplements that have been shown to have some potential of slowing/stalling prostate cancer (do a search or 2 online).
This means that there is no clear time limit for you, you have some measure of control, but it requires a very serious long - term sustained effort on your part.