In the field of sexual health the correct term is Erectile Dysfunction (ED). It affects 5-10% of men between 20 and 30, 40% of men over age of 50, and increases gradually with age. It can be separated into 2 forms:
1 - Organic ED - which is related to both systemic conditions ( diabetes, atherosclerosis, dyslypidemia, hypogonadism, smoking, low exercise) and local ones: abnormal venous drainage( it leaks too much-pretty rare) trauma in the past, infections, etc.
2 - Psychogenic - It is related to stress, Anxiety, Depression, low self esteem, many other triggers which can affect the neurophysiology of the male erection.
First one is mostly seen in elder ( 60% of ED from this group), The second one is mostly seen in young adults (60% of ED from this group). In many cases it is mixed. Also there is a link of pornography consumption to the development of ED , and different types of medications can cause it, not to forget some of the Fitness suppliments.
If you manage to get ED try to realise the problem if you can quickly spot it (ex: after break-up i can't get hard anymore: problem = the drama in your head, get over it and if the ED was psychogenic, you could have enough ressources to get rid of it yourself. If you smoke- stop smoking, start exercizing). If it persists (3 months or more) Go get medical help, you may need some blood tests to look for that conditions which may start with an ED bud after some time it may danger our life if not treatable (diabetes, atherosclerosis, dyslypidemia etc.) Get treatment and enjoy your life further. I have to mention that Medications like Sildenafil (Viagra), tadalafil...etc. have 90% of succes in treating ED.
I have much more to say but this is it for now.
Have a good day, or rather say... Night! Feel free to ask questions!