Shade's Children, Paperback/Garth Nix

If you're lucky, you live to fight another day. In a futuristic urban wasteland, evil Overlords have decreed that no human shall live a day past their fourteenth birthday. On that Sad Birthday, the children of the Dorms are taken to the Meat Factory, where they will be made into creatures whose sole purpose is to kill. The mysterious Shade--once a man, but now more like the machines he fights--recruits the few teenagers who escape into a secret resistance force. With luck, cunning, and skill, four of Shade's children come closer than any to discovering the source of the Overlords' power--and the key to their downfall. But the closer they get, the more ruthless Shade seems to become. . . .