Völsung's mother carried him in her womb for six years:
Now no otherwise it goes with the queen's sickness than heretofore, nor may she be the lighter of her child, and six winters wore away with the sickness still heavy on her; so that at the last she feels that she may not live long; wherefore now she bade cut the child from out of her; and it was done even as she bade; a man-child was it, and great of growth from his birth, as might well be; and they say that the youngling kissed his mother or ever she died; but to him is a name given, and he is called Volsung; and he was king over Hunland in the room of his father. From his early years he was big and strong, and full of daring in all manly deeds and trials, and he became the greatest of warriors, and of good hap in all the battles of his warfaring.
Source: The Story of the Volsungs, translated by William Morris and Eirikr Magnusson
Is there a reason for this extremely long gestation?