We usually think of coming-of-age stories as distinctly human-based—a youngster heads out into the great wide world and learns how to be a grown-up in the midst of all its troubles and strife. London takes that notion and applies it to a wolf, who has to explore the world, lose his innocence, and find out how tough life can be. There's also a clever reversal in White Fang. In most coming-of-age stories, the hero starts out at home and goes out into the world. Here, the hero starts out in the world, and—through his slow, painful, killing-a-lot-of-dogs-along-the-way path—eventually finds his way home.
White Fang's coming of age is different than the coming of age in a human. In fact, it's quite the opposite.
White Fang comes of age the same way that humans in other stories do. The only difference is the species.