This is my first message on this site. I chose this topic because sex is always interesting.
From strictly a clinical angle, the first thing that came to mind is the question, what is excessive masturbation? I would say that if someone masturbated multiple times every day that could be an indication of a problem, but not necessarily what people might think. One common problem for males is a condition called Epididymitis. This is when the spermatic cord, the epididmis, becomes inflamed. This can happen with prolonged sexual stimulation and no release. Masturbation can relieve this condition. I found this out when I was a Hospital Corpsman in the Coast Guard. The only way I can think of that masturbation would be excessive is if there were either a psychological obsession or a hormonal imbalance. I would think that if masturbation did not negatively effect one's life, there is no problem.
Masturbation can be a remarkably healthy practice. For males with a very strong libido and little or no outlet for sex, it can keep the libido under control. Not having this release can have extremely bad effects both physically and mentally. It can even cause a man to commit a sexual offense.
On a personal note; I can masturbate up to a dozen times a week. Though I'm 63 and have rheumatoid and fibromyalgia, they sure don't have any effect on my libido. Being so easily sexually stimulated gets really annoying at times. I often envy men who need Viagra. There's nothing worse than having a high performance car and no track to race it on. I was in a Platonic marriage for over 20 years. After separating, I'm stuck being disabled just enough where I can't get out to meet people. So masturbation has been a great way to keep my libido under control. There is absolutely nothing to be ashamed of.
Thomas