The human brain takes up to 25 years to reach full maturity, arriving at the finish line nearly a decade after the body is fully grown. In that gap between being big and being grown-up lies a lot of the best young-adult fiction, including Geoff Herbach's painfully funny debut, "Stupid Fast" (Sourcebooks Fire, $9.99, ages 12 and up).

Stupid fast is the only way to describe 15-year-old Felton Reinstein, a twitchy nerd known as "Squirrel Nut" to the jocks in his rural Wisconsin high school, who suddenly discovers his fast-twitch muscles during the 600-yard dash one spring. His sudden speed, round-the-clock hunger and capacity to sprout "a thousand pounds of hair" soon capture the attention of the town's football coach, who envisions a winning future for Felton on his team come fall. But his growth spurt is having an unsettling effect on Jerri ("who happens to be my mom but also a big hippie who doesn't like hierarchy," Felton explains), who begins a descent into full-blown depression. His little brother Andrew, who takes to dressing as a pirate during the highly dysfunctional summer that follows, suspects the troubles hinge on their late father -- who hanged himself in the garage a decade before.

This setup may seem awfully dark, even by the standards of young-adult novels, which feature a high per capita ratio of alcoholism, bulimia and vampirism these days. Fortunately Herbach, who teaches creative writing at Minnesota State University, Mankato, has a deft touch, making Jerri's descent feel entirely believable, while keeping her sons from falling with her into the abyss.

After all, Felton has a number of distractions -- delivering the newspaper for his friend Gus (away dealing with his own family troubles in Venezuela), coping with the sudden approval of the dimwitted jocks he once disdained, and figuring out how to repeat his first kiss with Aleah, the beautiful piano prodigy whose professor father is teaching at the local college. As Felton frets, "I began to worry that I'd never have another chance to kiss her. I mean, Jesus, how are you supposed to kiss someone if you haven't fallen over on the ground? Tickle fight? Tickle her. Tickle her. I didn't tickle her because it didn't seem respectful."

These funny but agonizing inner dialogues feel like a true glimpse into the teenage male brain -- whip smart, painfully self-aware and unbelievably wrong-headed, sometimes all at once. Young readers looking for a genuinely memorable first-person narrator -- in the vein of Sherman Alexie's "Absolutely True Diary of a Part-Time Indian" or Pete Hautman's "Godless" -- should really catch up to "Stupid Fast" this summer.

Laura Billings is a writer in St. Paul.