Forum:KB:how can Obi wan be old in New hop

Hi sorry the title is missing the E but i was thinking how on earth can Obi Wan Kenobi be an old man in New Hope or perhaps conversely how can the events of Phantom Menace happen in 32 BBY meaning that by 0 BBY or New Hope he is 57 years old either he aged real bad or there is a mis calculation in the dates by Lucas or whoever made the story. thanks