Neil Mockford/FilmMagic/Getty Images

Most teens his age are sweating school essays, but pop superstar Justin Bieber has already finished writing his second memoir. The book "Just Getting Started" is due out today.

"My life has changed so much within the past couple of years, and I wrote it so you could see all the behind-the-scenes in my world," Bieber said in a YouTube message to his fans ahead of the book's release.

Celebrity website Sugarscape.com has exclusive excerpts and photos from the book, but don't expect the 18-year-old to dish on everything.

In a nod to his relationship with fellow singing star Selena Gomez, Bieber writes, "There are just some things I am trying to keep private because I am young and figuring it out. I am learning about trust and the joys and struggles of it. I like being with someone who is smart and who I can have an actual conversation with."

Bieber also takes aim at overzealous paparazzi, writing, "But it's not OK when they come at me aggressively and don't respect my space. There's a misconception that I hate the paparazzi. I don't, I simply don't like the aggressive paparazzi."

The pop star has had several high-profile run-ins with photographers this past July. A scared Bieber even called police to report that he was being chased.

ALSO READ: Justin Bieber 911 Call: Police Were 'Not Nice' About Speeding Ticket Stop

In the recording, which was obtained by radio station LA96.3FM and posted on TMZ, Bieber sounds tentative as he tells the dispatcher: "Um, I have like, five cars following me," he said.

The dispatcher asks the 18-year-old star his name, and he replies: "Justin."

When she asks for his last name, he pauses, then answers, "Johnson."

Bieber made the call after he was ticketed earlier that day for speeding, and he's said he was driving fast to evade the aggressive paparazzi.

And earlier in May, Bieber confronted a photographer outside a movie theatre. But it's not just paparazzi that are the problem. While waiting for Gomez at a Toronto airport, Bieber also had words for some over-eager fans.

"Why do you have to be so impatient? I am a human being, do I not have the right?" an exasperated Bieber said.

Howard Bragman, an ABC News consultant from Reputation.com, said: "There is a price to pay and I think he talks about that in some depth. And the price he pays is giving up a lot of freedom."

And while some may wonder how an 18-year-old, even one who's a megastar, could have lived enough to have already finished a second memoir, the answer may lie with his millions of "Beliebers."

RELATED: Criminal Charges Filed Against Paparazzo in Justin Bieber Chase