In the information given for stage 4, it says that if ejaculation has not occurred earlier, it will begin in this stage. Does this mean that ejaculation is normally only supposed to happen in stage 2 or 4?
Also, does sexual drive (i.e. masturbation) typically decrease from stage 4 to 5?
The seminal vesicles have to reach a certain point of maturity to produce semen. For about half of all boys this happens during stage 2 of development. For the rest it happens during stage 4. Once it begins, it doesn't stop so a boy who gains the ability to ejaculate in stage 2 continues to experience ejaculations through stages 3, 4, and 5.
The male sex drive reaches its peak at the beginning of stage 5 and then remains steady or every slightly decreasing over the rest of his life. Therefore the sex drive increases during stage 4.