What is causing erectile dysfunction in a 20/y old?

Performance anxiety: Performance anxiety is major cause of erectile dysfunction in young men. Well, that & life style, eg smoking, excess alcohol, other illicit drugs, etc. Think of it as stress begets ed which begets stress which . . . Well, you get idea. In older (that's a relative idea) men, our (poor) health gets in the way, eg blood pressure, cholesterol, diabetes, etc. In both cases, don't forget partner, family.