Tripods: The White Mountains: Book 1 by John Christopher
Nobody knows how long it has been since the Tripods came. Nobody remembers life on Earth before they enslaved it. Humans live in scattered farms and villages, kept quiet and obedient by the mind-controlling Caps implanted when they reach their teens.
Will Parker's time is fast approaching - but a chance encounter with a madman convinces him that it may still be possible to resist the alien masters. So begins an epic tale of survival and defiance - and Will's journey to the White Mountains.