One of the things I have found baffling on the Peak Testosterone Forum is how common erectile dysfunction is in young men. We have just one young guy after another on the forum struggling in the bedroom. This is verified by recent stats that show that a very high percentage of younger males are struggling with E.D. In fact, one recent study showed that 1 out of 4 men under age 40 at an outpatient clinic in Europe had erectile dysfunction!. This is an incredible statistic as men that age are usually "unstoppable" in the bedroom and able to orgasm many times per day, etc. However, I have no doubt that the rates are similar here in the U.S. based on what I am seeing. Also, this same study showed that half of the above men under 40 had not just E.D. but severe E.D.
Clearly, this is a big issue and I have also been surprised to find that the reasons for erectile dysfunction are not necessarily as different from us older guys as you might think. Below I give you the Three Research-Backed Reasons for Erectile Dysfunction in Young Men:
1. Testosterone. I don't have any statistics, but I find quite often on the Peak Testosterone Forum that the young guys tend to have less arterial issues than the middle-aged or senior crowd. This just stands to reason due to the fact that a young man has had less years to damage his cardiovascular system through the typical Western Diet and lifestyle. (More on that below.) Although arteries are less often an issue, young guys are certainly not immune to the effects of low testosterone.
The good news is that it is at least straightforward to get tested for low T: it is a simple and relatively inexpensive test. You just get a blood draw first thing in the morning and you should have your results the next day. If only I had done this test in my 20's! I had many standard low testosterone issues: anxiety, depression and lack of morning erections just to name a few. These caused me many problems over the decades.
2. Atherosclerosis. Because of what I wrote above, you might think that young men rarely have artery-related erectile dysfunction like the middle-aged and senior men have. Of course, it is true that young men have less. That said, there is actually substantial evidence that MANY young men are suffering a loss of erectile strength due to arerial issues. I know that the traditional line of thinking is that this is close to impossible, because a young guy in his 20's or 30's could not damage his arteries that quickly. However, let me explain the evidence that that is simply not the case.
While it is true that we know that arterial plaque tends to build up slowly, what many men (and doctors) do not realize is that a Western lifestyle is almost designed to be hard on your cardiovascular system. And, after reading Heal Your Heart by K. Lance Gould I realized that young men can easily build sufficient atherosclerosis to reach the point where it affects nitric oxide output for reasons I will discuss below.
Dr. Gould provides abundant evidence that a high percentage of men in their 20's have significant atherosclerosis. For example, he cites one study of 21 to 26 year olds where they examined the bodies of men that had died of noncardiac deaths. 15 to 21 percent had the diameter of a major artery reduced by 25%! Now, granted, this is probably not representative of the general population, but keep in mind that these were noncardiac patients. 
And you may be wondering if a reduction of 25% in the diameter of a major artery would cause health problems? Is it really that big of a deal? Actually, a reduction of 25% would probably not cause standard heart disease symptoms. However, remember that the penile arteries have a much smaller diameter than the major neck and heart arteries. This is why men get erectile dysfunction BEFORE a heart attack or angina: these smaller penile arteries are giving a warning that there is underlying atherosclerosis.
So the key is that penile arteries can clog and lose proper blood flow before the bigger arteries. And arterial bloackages do not respect age or seniority. Therefore, some of these younger men were probably struggling in the bedroom and could not figure out why. And remember: it's not just a blockage issue. As the lining of your arteries (the endothelium) gets covered up in plaque, it loses its ability to pump out nitric oxide. And, as nitric oxide lowers, erectile strength and hardness factor falter.
Another interesting study cited by Dr. Gould was one of Vietnam War veterans back in 1971. Of course, these are generally young, very healthy males. This particular study found that 45% of them had atherosclerosis and their average age was 22!  Other studies on trauma victims and Korean War veterans had similar rates for guys in the 20's.  Gould lists a total of five more that he lists from prominent journals such as JAMA and Circulation that show that young guys in the 20's and 30's have a prevalence rate of between 41% and 77% for artherosclerosis. Ouch! No wonder so many die of heart attackes: about half of them have a ton of plaque in their 20's!
Are you a young guy that has lost some of his erectile strength? Are your morning erections weaker? Have you lost the ability to get spontaneous erections? Well, based on the above, atherosclerosis is something to look at as a possibility. And I mention it, because it not something that one's doctor will think of. He will probably just hand you some Viagra or Cialis and call it a day.
So how can you tell if you have atherosclerosis? This can be done through what is called a Calcium Score or Heart Scan without a doctor's orders in most locales for a minimal fee. (I had one of these last year and my cardiac arteries came back perfectly clear, due, more than likely, to the Low Fat Paleo Diet that I was consuming. You can read about it My Heart Scan Results if you're interested.) A Heart Scan does require some radiation though.
A less invasive way is through an ultrasound IMT of the neck artery. This is now available without a doctor's orders through Life Line Screening for a minimal fee. A good starting point to regression of plaque and improving blood flow is to lower both LDL and triglycerides. I recommend the above book by Gould and also Track Your Plaque by Dr. William Davis for a fantastic summary and discussion as to how to do that. You should also scan through my links on LDL Levels to Reduce or Arrest Arteriosclerosis and How to Increase Your Nitric Oxide Levels Naturally for additional information.
I also recommend using the new Berkeley Nitric Oxide Test Strips to get a gauge on your arterial nitric oxide levels due to food.
3. Psychogenic (Psychological). One very common problem for young men is psychogenic, or psychological erectile dysfunction. Of course, it is possible to have a combination of both physicial and psychogenice reasons as, in particular, some failure in the bedroom can really affect many men psychologically. Believe me I have seen young men depressed and/or nearly hysterical over the issue. It's a lot of pressure and - let's be honest - by far our biggest source of dopamine. In any event, you can read more about the subject in my page on Psychogenic Erectile Dysfunction.
2) Heal Your Heart, Rutgers Univ Press, 1998, by K. Lance Gould, p. 43.
3) JAMA, May 17 1971, 216(7), "Coronary Artery Disease in Combat Casualties in Vietnam"
4) Circulation, 1995, 91:1706-1713, "Occult and Frequent Transmission of Atherosclerotic Coronary Disease With Cardiac Transplantation"
5) Heal Your Heart, Rutgers Univ Press, 1998, by K. Lance Gould, p. 44.