There are strict conditions for joining the party. He seems to have to apply for his age in his twenties.
It seems that there are various routes to join the party, but it belongs to an organization called “Assault Squadron”, and it seems that joining the party is guaranteed by working.
If you work safely and get discharged, you will be guaranteed entry to the Workers Party. If you want to go on to university, people from the People’s Army can only go to general universities, but if you are from an assault squad, Kim Il Sung University or Kim-Song Political and Military University (now Kim Jong-il Political and Military University ) which trains senior military officers. Although his enlistment is highly competitive, his father is a revolutionary and a native of a railway college. He has a background as a corporate culture instructor. (Hai Eikichi, North Korean Bad Diary)
If they work in an assault squad for a year, they will receive a recommendation to become a party member.
If you work as an assault squad for one year, you can get a recommendation of a superior and become a Labor member. (Shin Young-hee, “I was Kim Jong Il’s Dancer”)
In addition to the assault squad, they can join the party by serving in military service.
Those who do not work for military service in North Korea are not included in the Workers Party of Korea. Not being a Workers Party member means that in North Korea it is a slave and language-speaking tool working for Workers Party members. (Ju Sung-il, North Korean People’s Army: Living Hell’s Hyoei, translated by Kim Ryumori)
However, it is said that there are some cases where joining the military does not allow them to join the party.
It is not easy to join the Labor Party. It is the reality that working in the military for 13 years often does not allow them to join the party. (Ibid.)
In addition to the conditions for entry, there seem to be characteristics and tendencies of those who are preferred as Workers Party members.
The hospital had a restriction that only four doctors would allow one person to join the party, but it seemed quite natural that Dr. Kim was elected. For one thing, women tended to be favored as party members, as most women do not drink and adhere to the rules. Dr. Kim’s discipline and the somewhat square shape were perfect for future members. (Demick, op.cit.)