Unable to get erect. For lack of a better description, erectile dysfunction is the inability to obtain & maintain an erection (hard on) adequate for sexual activity leading to distress. Note that w/o distress, there is no dysfunction. Ed has many causes that should be considered & treated rather than masking w/medications, although these new drugs have revolutionized treatment.
Depends. Symptoms of erectile dysfunction is exactly that, having difficulty obtaining and/or maintaining an erection during periods of sexual arousal. Low sperm count is not necessarily associated with any specific symptom. A semen analysis directly assesses the sperm count. Sperm count and erectile dysfunction are not necessarily related. You can have one without the other.
The symptoms of Erectile dysfunction include: Inability to attain an erection, Inability to sustain an erection.
Erectile dysfunction. Difficulty getting and/or maintaining an erection.
Same as in older man. By definition, erectile dysfunction is the inability to attain and/or maintain an erection adequate for sexual activity to such a degree that it causes distress. Age is irrelevant in the definition but distress is a requirement. If the lack of an adequate erection does not cause stress, then you don't have erectile dysfunction, regardless of age.