Books in Heinlein's Future History series

Members of the Families were ordinary human beings, no different from neighboring Smiths or Browns, except for one disturbing trait: they were extraordinarily long-lived. In the ultra-civilized year of 2125 A.D. this distinction was intolerable. Hounded for a secret they did not knowingly possess, the Families were forced to choose - torture and extinction by their jealous, short-lived fellowmen ... or flight from Earth on an untested starship. They chose the latter. But to their horror they discovered that the alien stars nourished a threat even more terrifying that the one which had taken them from Earth.