Why ask such a question? Wasn't he seen recently in public with his dad Kim Jong Il?
Well yes. However, when and where was he born?
Daily NK explains that none of this is new.
Well there is NO official birthday, birth year or birth place for Kim Jong Un, yet. However, some sources in the Democratic People's Republic of Korea (DPRK) claim that this is being manufactured at present.
It goes like this:
Kim Song Ju (Kim Il Sung after 1935) was born 15 April 1912 at Mangyongdae near Pyongyang. His birthplace is a national shrine, although the authenticity of almost all of it is questionable, debate about his birthday, birth year and birth place is largely closed.
Kim Jong Il was born 16 February 1941 at Vyatskoye Russia. This is where it gets interesting. The official story is he was born 16 February 1942 at Mt. Paektu in Japanese occupied Korea. The earlier date and location are proven by Soviet records and other historical accounts. Even the DPRK once published his birth year as 1941 well before Kim Jong Il had any political role.
Why change it?
Firstly the change in location is the most important point. The official history of Kim Il Sung is that he was an anti-Japanese revolutionary fighter (true on the face of it) who helped lead the Korean people to remove the Japanese Imperial Army from the Korean Peninsula (far from the truth). To support this myth it can't be said that Kim Il Sung in 1941 (or 1942) was actually in the USSR leading the 1st Battalion of the Soviet 88th Brigade of exiled Koreans (and Chinese) learning about Marxism-Leninism. Kim Il Sung fought in the Red Army, a fact that would not support his nationalistic Korean anti-Japanese credentials. Those credentials have been critical to gaining support for him among north Koreans - who better to lead you than a man who single-handedly saved Korea from the (truly) brutal and barbaric Japanese occupation.
So Kim Jong Il HAD to be born in Korea to support the myth of his father. Given that was the case, where better than Mt. Paektu, the highest mountain in Korea (although half of it is in China) and so it carries "sacred" qualities. It is where Kim Il Sung was supposed to have had his base to fight the Japanese, so how better to assert anti-Japanese credentials for Kim Jong Il than to claim he was born amongst soldiers.
What about the year? Well Kim Il Sung was born in 1912, which meant 1962 was the year of his 50th birthday celebrations. It was decided if Kim Jong Il was said to be born in 1942 not 1941, then 1982 could be a year of 70th birthday celebrations for Kim Il Sung and 40th birthday for Kim Jong Il (he was publicly announced effectively as successor by name in 1980). Nothing more than that.
So Kim Jong Un? He needs a suitable birthplace, something to do with his grandfather I would think. There are conflicting accounts as to whether this is being constructed (and residents relocated as a result). The birth year is accepted in South Korea as being 1983 because of the testimony of Kim Jong Il's former chef who defected. Shifting it to 1982 would align it with his father.
What does all of this prove beyond being a quaint curiosity? That a state that owns its people so comprehensively as the DPRK is so egregiously willing to lie to them on such a grand scale about the most trivial of things.
On a more optimistic note, the Korea Times reports that North Koreans are laughing off the propaganda they are being fed about the new leader and his immortal exploits. Given even his older half brother opposes the succession (and is being protected by the Chinese government), it seems unlikely that a second hereditary succession can be undertaken smoothly.