When he was 14 , Ramesses was appointed successor by his father Seti I. He ruled Egypt from 1279 BC to 1213 BC . p165 This is a total of 66 years and 2 months . At age fourteen , Ramesses was appointed Prince Regent by his father Seti I. He is believed to have taken the throne in his late teens and is known to have ruled Egypt from 1279 BC to 1213 BC for a total of 66 years and 2 months , according to both Manetho and Egypt 's contemporary historical records .