The Atlantic's Brian Fung has the details:
At a news conference in Tokyo, Fujimoto let slip the North Korean leader's birthday -- a date that has, until now, lived in obscurity: January 8, 1983. That makes Kim 29 years old, and just a month shy of 30. The next-youngest serving world leader is Jigme Khesar Namgyel Wangchuck, the king of Bhutan. He's 32.
But where is his birth certificate?