YA/teen book with male main character meeting his future self who wants to fix history

Question

Currently looking for a book with a male teenager protagonist. Possibly a secondary female protagonist.

He meets his future self who has come back to “fix” history. This includes killing people who he thinks are responsible. In the future self’s attempts however, he makes the future worse and forgets that he already attempted to “fix” it. The future self goes insane and the protagonist must find how to stop the damage. He uses an “information helmet” from the future and realizes he can’t become an engineer like he wanted to be.

I distinctly remember the protagonist deciding to “never become an engineer” in order to prevent the technology from being invented.

I read this maybe 2005-2010, it was a school library book (USA). I’m recalling something about a mirror being used to communicate. I didn’t find it on the Wikipedia page for time travel books. Written in English.

Answer 1

I am almost positive this is The Time Shifter by John Peel.

A beautiful dream of a better future? Or Brandon's worst nightmare...?

Twelve-year-old Brandon Mooney gets the scare of his life when he looks into a mirror...and sees a grizzled old man staring back at him! But things get really weird when the old man steps out of the mirror and introduces himself as Brandon Mooney...age 92!

No way! The old Brandon has traveled back in time 80 years. Why? It turns out the future isn't as great as it was cracked up to be. In fact, it's the pits. So the old man has decided to step back into the present in order to change the future--and he needs Brandon's help.

As Brandon will discover, however, tampering with time can have some unexpected--and very dangerous--consequences.

It was over a decade ago when I read it, but I remember the old Brandon assassinating many people, and the young Brandon learning that the world turns bad because of the industry to create the time travel device he invents as an adult. The book ends with him declaring he won't go into computing, but instead become a marine biologist, which reverts all of the terrible things his older self had done.