This is another debated topic. I don't think it's hereditary either. However, it might be possible to become one I suppose but drinking the blood of another is not the way. A lot of people might think they became a vampire because something in their life happened that made them realize they are. This can happen anywhere from childhood to adulthood.
Most people realize they are in their late teens early twenties.
As far as what proof, I have, there is none. I don't know what kind of proof you want because when it comes to the net, anyone can make up anything. You have to take everything with a grain of salt. I could say, I am a real vampire because of such and such but that still wouldn't do anything. Whether I am real or not doesn't make a difference.