A single step or stage in the succession of natural
   descent; a rank or remove in genealogy. Hence: The body of those who
   are of the same genealogical rank or remove from an ancestor; the mass
   of beings living at one period; also, the average lifetime of man, or
   the ordinary period of time at which one rank follows another, or
   father is succeeded by child, usually assumed to be one third of a
   century; an age.