Shade's Children by Garth Nix

Gold-eye is a young boy who lives in the 'Dorms' where all children under the age of fourteen must reside, kept in check by implants called tracers. In this futuristic wasteland, no human over the age of fourteen is allowed to live as made law by evil Overlords. Gold-eye avoids this fate by breaking out of the Dorms and meets fellow escapees while being hunted by mutant creatures sent out to re-capture--and possibly kill--him. These escapees call themselves 'Shade's children' and are working with the mysterious individual Shade to free themselves from the reign of the evil Overlords. Gold-eye joins them in their quest, but all is not as it seems and they soon find themselves questioning Shade's real motives in his almost desperate gathering of information.