How is this a coming of age story?

In some ways Montana 1948 is a bildungsroman detailing David’s transition from boyhood to manhood, and the end of his childhood innocence. This transition has three facets to it. The first is David’s sexual development, as he transitions from his chaste love and crush on Marie Little Soldier to more sexual and lusty thoughts about his Aunt Gloria and Loretta Waterman, a high school girl in his town. The second is David’s exposure to violence, first when he kills the magpie, but also when his grandfather’s men try to break Frank out from the basement. After that day, it seems useless to protect David from evil and danger, when they are “so near at hand” (Watson 153). The final facet is David’s disillusionment with justice and the rule of law. After the events of 1948, he can longer harbor his naive belief that good deeds are rewarded and bad deeds are punished. Looking at his parents, he sees that even when you do the right thing, you can suffer negative consequences. Looking at his uncle Frank, he sees that criminals don’t always get an apt punishment or even their day in court. And looking at Marie, he sees that justice isn’t always served for those who deserve it.