Kim Jong Un has turned 40, but he's forgoing a big celebration. Experts say he probably feels like he hasn't achieved enough for his age.

• Kim Jong Un is thought to have turned 40 on Monday, according to the US.
• But he's skipping public festivities, with nothing scheduled or publicly announced.

Kim Jong Un is thought to have turned 40 on Monday, according to the US government. However, he seems to be forgoing a big celebration.

An expert on North Korea told The Associated Press that the North Korean leader may be skipping national festivities because he doesn't believe he has achieved enough for his age.

Hong Min, an analyst at Seoul's Korea Institute for National Unification, told the AP: "For Kim, it's still probably politically burdensome to idolize himself as he's still young and hasn't accumulated much achievements."

According to the AP, some have posited Kim may think he's still too young or believes he needs greater accomplishments to his name to justify hosting the extravagant celebrations associated with his father and grandfather.

The birthdays of his father, Kim Jong Il, and grandfather Kim Il Sung are two of North Korea's biggest holidays, traditionally marked by tributes and fireworks, as well as occasional military parades.

But the younger Kim, whose official birth year has never been confirmed by the North Korean government but is believed by the US to be 1984, has no public celebrations planned.

Kim Yeol Soo, an expert at the Korea Institute for Military Affairs in Seoul, told the AP that Kim's birthday may take some time to merit an official holiday.

This is because North Korea's ruling elite views him as not senior enough, he said.

However, the AP noted that Kim's father's birthday became an official holiday when he turned 40.

Another reason the North Korean leader might be forgoing a national party is that it could draw attention to his Japanese-born mother, Park Won Gon, a professor at Seoul's Ewha Womans University, told the AP.

"The fact his mother came from Japan is his biggest weak point," Park said.

Kim's mother, Ko Yong Hui, was his father's third or fourth wife and was born in Japan, which historically colonized the Korean Peninsula. Her background is considered disadvantageous to Kim's rule, the professor added.

Though the North Korean government has never confirmed Kim's birth date, two occasions have seemingly suggested that it falls in early January.

In 2014, the former NBA star Dennis Rodman sang "Happy Birthday" to Kim before a basketball game in Pyongyang, North Korea, the AP reported.

And Reuters reported that then-President Donald Trump wished Kim a happy birthday in January 2020, with North Korean authorities acknowledging the message.