See my comment ;)

Interesting. I'm 19 at the moment and have only experienced Psychological E.D. ONCE.
How much are we talking about when we say "too much" or "over-use", though?

I attributed my ED to anxiety and/or alcohol use to begin with, but after experimenting with a girl that I had told about the situation, for me it was clearly desenitization. It depends on a few different factors, really. I read stories of people that fapped up to 5 times a day and people that were prone to binge and chain-fap every few days. I was more consistent, having a fap daily or twice a day, but a larger contributor to my ED was the increasing extremity of the content of the porn I was watching. More extreme = more exciting = more desensitization to the real thing. The way you fap is another factor too - check out 'your brain on porn dot com' for more info if you wish :>