Scythe by Neal Shusterman
Most people in this future utopian society are content, but are their lives still meaningful? Death and old age are now reversible conditions, except for those gleaned by an order of scythes. Feared and celebrated, scythes can grant a year of immunity. Teens Citra and Rowan are selected to be apprentices to Scythe Faraday, but only one will be chosen to be a scythe. This is a unique, astounding blend of philosophy and high-octane adventure. First in the Arc of a Scythe trilogy, this book is deservedly popular with teens and adults. The sequels are Thunderhead and The Toll.