I read an article on the study you referred to and what come to my mind is correlation does not equal causation. Just because two things happen together doesn't make them cause related. For example guys who masterbate more may naturally have more hormones. This increase in hormones may be the cause of the prostate issues not the masterbation itself. It could also be that in societies where there is higher masterbation there is more indulgence in other societal things like fast food consumption. It may also mean that guys who don't masterbate frequently (which would be the minority) take better care of themselves. It is something that warrants more studies but is not in any way conclusive.
Most of the research I've seen states that it is a health, normal, immune boosting, stress reducing thing. If you were up to say 3-6 times a day, then I would say you may want to cut back, but once a day is pretty standard.
If you are really worried than maybe cut back to every second day, but I wouldn't cut it out altogether as I think that would be far more detrimental to your physical health, and mental health as well.
If masterbation in your 20's was a sure fire way to get prostate cancer - almost every man would have prostate cancer, and they don't. Population studies like these are important for further exploration but people tend to misread them and journalists vying for a headline exploit them.
I would say you are perfectly normal, and if you are really worried about cancer risk than lead a healthy lifestyle and exercise and that will counteract any negative cancer risks associated with masterbation.
Hi as you have found many conflicting reports on masurbating, well in that case I should have a prostate by now, I woul think masturbating 2/3 times a week would be best, as over masteurbating can run men and young men down and then they get ED.
Look if you think its not doing you any good, men who have porn enduced ED are advised to take 8 weeks off, that refraining from all forms of sex for 8 weeks, this gives the body time to reboot, and could ony help you then if you think your over doing it.
Good Luck