Because the females live in tight-knit matriarchal structures made up of mothers, daughters, sisters, etc., it is a very selective process since the males have to come into the herd from the outside.
Once a male has chosen the "woman of his dreams," he flaps his ears violently back and forth to communicate with the female and other males that he views as potential competition.
Because this is such a selective process, the younger, weaker males generally cannot match up with females their own age! It is not until they are much older and stronger are they able to mate!
Mating between male and female elephants is basically a game of tag! The females will run away from the males until they are ready.