An evil, despotic ruler orders all persons of your Race, birthplace, and approximate age put to death. As far as you know, you are the only one to escape this heinous act. (work with your DM to determine details)
The followers of an unheard-of-god from another land followed omens that led them to you. The omens indicate that you are to be the mate of an avatar (earthly incarnation) of their god. You disagree but are still harassed by the god's followers.
Approaching adulthood you experience wanderlust and decide to travel, roll 1d6 to detirmine years spent travelling and think about where your character might have gone. (work with your DM to determine details)