What would cause erectile dysfunction in a 25 year old male?

It is a common myth that impotence or erectile dysfunction is inevitable with age; this is simply not the case. Impotence can be developed at any age and can be a wide range of reasons, including psychological and physical. The first thing that I would suggest is to visit your own doctor so that any physical reason could be discounted with testing. This can be very helpful and tell a lot about your condition to a doctor as well as helping to identify any newly formed condition to which impotence can be an early indicator, such as Diabetes. With physical reasons no longer a factor after testing then the cause would be psychological. At such a young age it is more than likely that you are suffering with some form of performance anxiety or other psychological ailment which is having this detrimental effect on your sexual function. If indeed it is psychological than that is good news, as it is more than likely that impotence will only be temporary in your case and until your sexual function returns to normal a doctor may be able to prescribe you with Viagra or an alternative equivalent so that you can still continue with your sex life despite your temporary erectile dysfunction.