In the trilogy, people are Capped at age fourteen, which is also the age of majority. At first, making the age of majority so young seems like a hand-wave to justify some of the most important actions of the story being undertaken by teenagers. However, the lowering of the age of majority makes perfect sense when you realize that a lot of things that are necessary for adulthood — experience, self-control, judgment, — are not necessary for people who are brainwashed so that the alien mind control does their thinking for them and controls their actions.
Well, it's not just that. Ever heard of rebellious teen years? If you put off capping your slaves for too long, you'll end up with an army of angry, rebellious teenagers. Originally the age was set to when a human was fully-developed (specifically the skull and brain were), but this proved to be too dangerous, due to teenagers putting two and two together and refusing to be capped. The age limit was low, because doing it later was too risky. In the book there was even talk of lowering the age again!
It's also worth remembering that the world, or at least Europe, had been reverted to a Medieval Stasis. In the medieval era, there was really no youth culture to speak of. They couldn't afford it. The only purpose of youth was to learn a trade and prepare for their eventual role in adulthood, which could vary depending on whether or not you were a boy or girl, a firstborn, middle child, or youngest, ect. So children typically served as apprentices, pages, handmaidens, or squires. Being rural, non-technological, and parochial, they had no larger world as a reference, so seeking adventure might be limited. Not impossible, but it may not be always as easy as "steal some food, steal a horse, and off on a great adventure to wherever". It seemed very conveinent that the boys were always able to steal food quite easily. Medieval pantries were typically in the most secure areas of castles or villages and often under lock and key. I won't even mention how probably unrealistically easy it was for them to steal horses (a very important financial asset in medieval times).
Real medieval people secured their food and especially their horses quite well, but real medieval people didn't have mind control hats surgically welded to their heads. When everyone around you is having complacency, incuriosity, and obedience beamed into their heads all the time, you may worry less about being robbed. In the world of the Tripods, the only people likely to rob you are children and Vagrants. Children don't (usually) move around much and are known to everyone in the immediate community. Vagrants are already viewed with suspicion along with pity, perhaps in no small part because they just might do unimaginable and disorderly things.
Also, human beings tend to anticipate each other's behavior by putting themselves in another person's shoes. If you have a Cap suppressing your own impulses towards disobedience, greed, and lateral thinking, you may have trouble anticipating the actions of a thief and protecting yourself against him, even if the idea of being robbed crosses your mind.
It may seem strange that the Masters have a rather elitist, patronizing outlook toward humanity, not unlike pre-20th century Europe had to the rest of the world, while also being so technologically advanced. However, Will's Master states that their species were always united as one, there was never a period in their history they were split into competing nation-states. This means it's unlikely any group of them was ever oppressed by another, and thus the species as a whole never "learned the lesson" of why oppressing other people/races/species is bad.
In addition to this, the Masters probably view humans as backwards savages who need a firm hand, lest we go back to killing each other once again. With that view, they may have decided that it doesn't matter if they genocide us or we go to war with each other, since we're doomed either way.
Not sure if this would count as Fridge Brilliance or Fridge Horror, but I decided to choose the latter. Early on in the prequel, it is mentioned that during the first wave, the American Tripod just stood around doing nothing but then self-destructs. Later when the Trippy Show hits the air, the hypnotist mentions that the Trippy Show was made in the United States but that the hypnotic signals come from space. It is later stated that the Trippy Show was probably made by the first Trippies. Given the fact that the show originated in the United States and the fact that the American Tripod wasn't destroyed by the military, this seems to imply that the American Tripod was actually doing.....something to possibly some nearby folks or a TV station to hypnotize them into making the Trippy Show before it self-destructed. All these years of reading The Tripods, I never realized this until now.
