I guess our bodies are all different. I went vegan 1.5 years ago and I also feel better than I have in 20 years. Although I am not really vegan as I do eat sardines and take fish oil. Biggest challenge to a vegan is getting enough protein.
I would suggest picking up Dr. Gregers' book "How Not to Die" and reading the chapter on prostate cancer.
Also would suggest listening to podcasts by Rhonda Patrick on diet and exercise . And for more on health practices based on science, Hubermanlab.com.