Scythe by Neal Shusterman

The world has conquered disease, hunger, war, and death.  To deal with the challenges of immortality and crowding on the planet, only scythes can take lives.  Scythes can glean people from the population. Honorable Scythe Faraday has taken on two apprentices, Citra and Rowan.  This is unprecedented!  If they fail their apprenticeship, it could mean the end of their lives. There are those is Scythedom that would do anything to see them fail. Scythes must follow The Scythe Commandments, but there are some up-and-coming scythes that are challenging these edicts and pushing the limits of their power. This clash of old ways and new ways will not be beneficial for H.S. Faraday’s apprentices!