Are the War Boys just kids with radiation poisioning, were they bred that way, or was it something a regular person transforms into once you join Immortan Joe's clan? There were also "War Pups", so I was thinking the Boy/Pups were more like child soldiers.
The warboys are chosen from the masses of the wretched that live at the bottom of the citadel and wait for Immortan Joe to give them water. A deleted scene shows the warboys being selected with their parents wanting them to be selected as this is their best chance for survival in this world. They are chosen from a young age, and become war pups then when they are old enough become war boys.
They worship Immortan Joe and if Nux's behaviour is anything to go by live to be noticed by him before going out bravely in order to enter Valhalla
The lymphomas that many of the war boys show are symptoms from living in a radioactive wasteland and the use of "blood bags" is to transfuse healthier blood into themselves.