Vampirism is both a state of being and a life path. All true vamps have their own time line in their awakening and the development of any abilities. Some vamps know of their energy needs early in life and some later. I knew as a child about my bloodlust when I would hide in a closet to be alone and away from prying parents and feed upon myself. I noticed my pranic and psychic energy needs later as a teen in crowds while at music events.
Vampires are energy feeders and feed off the blood and psychic and pranic energy of others.
This need varies among all as does the level of ability. Blood energy feeds us, it does not make us. Blood is energy for the energy feeder. Blood contains many compounds and easily will make anyone to vomit when ingested too much. All vamps who are energy feeders of blood have their own levels of need and tolerance.