Immortality is discovered literally by accident, two factions of long-lived people exist, more information would probably have sorted most of the problems.
Perfectly adequate PNR. In this world, some people carry a genetic marker that produces a "change" in them between the ages of 28 and 32: They become unbound, no longer subject to the "boundaries" of time. They begin to age 1-2 years per century, no longer need to eat, and can only be killed by co...