At what age does the doctor start doing vasectomies?

I went to the hospital wednesday for minor surgery on my face, I got a birth mark with a small spot that was growing on it, Anyway after I went for a consultation for a vasectomy, And the doctor said I was not able to get one because I am 20 and I am still a virgin, the legal age is 19 around here, so I was just wondering at what age does the doctor start doing vasectomies? I made the choice not to have any kids myself, because I do not plan to have a very rich life and I am afraid I might not be able to support anybody else but me.