ED is more common in men over age 65. But it can happen at any age. It’s normal for men to have changes in erectile function, such as taking longer to get an erection. The older you are, the more likely you are to have ED. About 5% of 40-year-old men and up to 25% of 65-year-old men have ED, the NIDDK says. But it does not happen to every man as he ages.

In older men, ED usually has a physical cause. This could be a disease, injury, or side effects of medicine. Any disorder that harms the nerves or blocks blood flow in the penis may cause ED, the NIDDK says. The most common cause of ED is damaged nerves, arteries, smooth muscles, and fibrous tissues, often as a result of disease. Diseases like diabetes, hypertension, kidney disease, chronic alcoholism, multiple sclerosis, atherosclerosis, vascular disease, and nerve disease make up most ED cases. Up to half of men with diabetes have ED.

Other common medicines that can cause ED include tranquilizers, appetite suppressants, and the ulcer medicine cimetidine.

Testosterone helps the erection process. Levels begin dropping in men after age 30.

For years, healthcare providers thought the main cause of ED was psychological. But today most providers and researchers think that 80% of cases are physical. Psychological causes might be anger at a spouse, guilt over normal but "unfaithful" sexual interest in another person, or stress and burnout at work, experts say.

If ED is caused by a disease, medicine, or something else, that cause should be treated first. Oral medicines are available to treat ED. These medicines are not aphrodisiacs, so they have no effect on sexual desire. They relax the blood vessels of the penis. This allows it to fill with blood and to stay erect long enough for intercourse. These medicines also may cause side effects, so they aren't for everyone. Healthcare providers often prescribe both medicine and counseling. This is because couples seeking help for ED may have emotional issues they need to overcome, as well as the physical problems. Another treatment for ED is injection therapy, in which medicine is injected into the penis. Other treatments include inserting tiny pellets into the penis, putting bands on the penis, using a vacuum tube, and having a surgical implant. If low testosterone is causing the ED, it can be treated with testosterone patches or injections. In rare cases, surgery may be needed to help blood flow to the penis.