Kim Yo-jong, who is believed to be 26, is named a vice department director in the ruling party’s central committeeNorth Korea revealed on Thursday the official title of Kim Jong-un’s younger sister, who is widely tipped to become a close and influential aide to the young leader.Kim Yo-jong, believed to be 26, made her first public appearance during the funeral of her father and longtime ruler Kim Jong-il in December 2011.