What is less often discussed is the fact younger men can be susceptible too. While it's hard to know the precise proportion, not least because so many men are too embarrassed to see a doctor, what we do know is that many 20- and 30-somethings are suffering in silence.
One study found that ED affected 26% of men under 40, half of whom had severe ED. Other research, from the Massachusetts Male Ageing Study, has suggested that the proportion of men with mild or moderate ED correlates roughly with their decade in life (50% of men in their 50s, 70% of men in their 70s, etc).
More headline-grabbing was a recent study by Co-op Pharmacy, which suggested that 50% of men in their 30s struggled with ED (the highest percentage of any age group). Almost half these men cited stress from their work and personal life as the culprit.
Though this study may not pass muster scientifically, it does at least point to some explanations for what's occurring - namely that among younger men, the causes are less likely to be physical.
As Dr Anand Patel, a GP specialising in sexual problems, explains, the younger the man is, the higher the probability that the ED has a psychological component.
"It's very difficult to get large sample sizes of young men who admit to not being able to get a good erection - it's not something that's really talked about," he says. "But there's a ballpark figure that 40% of 40 year-olds and under are complaining of some sort of erection problem. Of that 40%, 60% will be psychological, so a large proportion will be anxiety-related, or there's a porn problem, or depression, which reduces your libido."
Clinically speaking, ED is classed as a constant or recurrent ability to maintain an erection. This means if you have the occasional off night (perhaps under the influence of drugs or alcohol) there's no cause for concern. However, if that 'off night' sparks performance anxiety, leading to a pattern of off nights, it's wise to look into getting treatment.
Physiologically, what’s happening is quite simple. When you're feeling anxious, your body releases a surge of stress hormones such as adrenaline, the 'fight or flight' chemical. This narrows blood vessels, reducing blood flow to the penis.
With depression, you may experience a loss of interest in activities you normally enjoy (including sex), along with sadness, fatigue and a sense of worthlessness. This is hardly conducive to optimum sexual function. In one 2015 study, 12.5% of men being treated for sexual disorders also had depression, and nearly a quarter had anxiety.
"If you're an anxious person you might want to speak with your GP about getting cognitive behavioural therapy," says Patel. "If therapy isn’t working quickly enough or isn't available, you could start anti-anxiety medication or antidepressants, but unfortunately these can have some sexual side-effects. You might take much longer to ejaculate or experience a reduction in libido."
He points out that there are other medications available that don't have these undesirable side-effects. If you think your medication is contributing to your ED, talk with your doctor.
Is porn to blame?
Beyond these kinds of mental health problems, Patel thinks there's another common culprit for ED in younger men, namely porn-induced erectile dysfunction (PIED).
Whether this is a widespread phenomenon, we don't know - cause and effect can get jumbled here, and it's hard to say whether the ubiquity of porn truly leads to higher ED rates. However, for a minority of men the pattern holds. They can easily maintain an erection while watching porn, only to struggle with a partner.
"When you're in your teens watching pornography, that is your learned sexual experience," explains Patel. "It becomes your brain's way of relating to sex and it's hugely problematic, because making love to your laptop avoids all the social nuances and physicality of having sex."
Not only does porn lead to unrealistic expectations about sex (including what your own and your partner's bodies ought to look like), it can also mean you get used to self-stimulation and become less responsive to the sensations of intercourse. Patel also thinks it can prime you to respond first and foremost to novelty.
"With porn you're going from video to video, and from new person to new person, which is highly arousing," he says. "When you try to translate that into real life with one single person, that relationship can decrease its value in terms of novelty and excitement and become less arousing."
If your porn use is causing problems, it may be helpful to see a psychosexual specialist (your GP should be able to refer you). You can also visit websites such as Your Brain on Porn, which recommend abstinence. The idea is that you treat the addiction by stopping the stimulus.
It's worth mentioning that while ED in younger men is commonly psychological, that isn't universally the case. According to one recent study, cardiovascular and metabolic risk factors are often under-looked among this age group.
"It would be unlikely for a young person to have a heart problem or cholesterol problem. but not impossible," says Patel. "And it's uncommon for a 20-something to have such bad diabetes that it damages the nerves to the penis, but I have seen it happen. Kidney problems and liver problems can also contribute to erection problems."
Another possible issue is Peyronie's disease, where there's a significant bend to the penis, caused by scar tissue. And if you've always had a problem getting an erection, it could be that the blood flow to your penis is somehow restricted. This is not to mention the unhealthy lifestyle choices (a bad diet, smoking, not enough exercise) that can affect vascular function.
"There are also some genetic conditions where your testicles don't make much testosterone - that might be an issue in itself," says Patel.
He adds that, while Viagra and similar medications help many men with ED, for proper sexual functioning it's important to address what's truly going on.
"Some people with erection problems take Viagra and get their erections back, but as they get older they find their erections start to go away, even with Viagra. That's because they don't really know what they're aroused by," he says.
In essence then, if you're struggling with ED there could be a number of different issues at play, and what holds true for you may not hold true for someone else. It's worth setting aside any embarrassment and having an honest conversation with your doctor.