It might be The Terminals, by Royce Scott Buckingham.
>When 19 year-old Cam Cody is diagnosed with a terminal illness, he expects to spend the rest of his shortened life in an adjustable bed. Then one night, a mysterious man offers Cam one chance to join a covert unit of young "terminals." They are like him, only they spend the last year of their lives executing exciting and dangerous missions to make the world a better place.