Masturbation at 20-30 's increase the risk of prostate cancer. While at 50's it lowers the risk. Is it true?

Just not true. It would be difficult to find a control group. There's not a shred of evidence that this is true. The claim that young men give themselves cancer in this way was made up by one of the cults to frighten vulnerable teens. "Heroic abstinence" is strongly suspected as a risk factor for benign prostatic hyperplasia but obviously we can't do controlled studies. I'm sorry people lied to you.