You are mistaken for the missing offspring of the ruler of the land and are taken to live in the ruler's household. After 1d6 years something happens that causes you to leave. (work with your DM to determine details).
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)