North Korean leader Kim Jong Un is believed to have turned 40 years old, though the milestone was not publicly acknowledged in the secretive country. Kim’s birthday has never been revealed to the public, but if speculators are correct, he celebrated the event on Monday, the same day official pictures were released of him visiting a chicken farm with his daughter. According to BBC News, the birthdays of his father Kim Jong Il (Feb. 16) and grandfather Kim Il Sung (April 15) are celebrated as national holidays in North Korea. Kim, who took over as supreme leader in 2011, has not celebrated his b…