What is the cause and treatment for erectile dysfunction? my husband taking too much time for erection and some times not achieving erection at all.

Take him to his doc: Since you are 21yo, i'm going to assume that he is about your age. In that case, it is less likely for erectile dysfunction to be due to medical condition such as diabetes, high cholesterol, etc. More common in this age group, stress eg work, relationship (how are you two getting along?), family, money, tobacco, excess alcohol are issues. If none of these, then go see family doc for evaluation.