When you talk about “the age system” in Korean, you could be referring to one of two things. You may be talking about their birthdays and how old they are. However, you may also be talking about the makeup of the society and how it functions because of age. I will address both so you can understand age in Korea a bit better.
In Korea, people are thought to have age before they are born. In the west, when a baby is born, the baby is 0 years old, but when a baby is born in Korea, he is one year old because they count the time the baby was alive in the mother’s stomach. When the lunar New Year comes at the end of January or first of February, everyone in the country has a birthday and becomes a year older. That means that If a baby was born at the end of the year, they can be only a couple of days old or a month old, but when the lunar New Year (Solnal) comes, they are considered a year older, so that newborn baby may be 2 years old at that point.
Now, if you are talking about who is in charge in terms of age, who ever is older is in charge, even if it is only one hour older. If you are with a group of friends who all seem the same age as you are, but you realize you are the oldest, you have the right to boss them around, and they let you. If there are two brothers or sisters, the older one is always the boss. the younger ones are very subservient and don’t go against the culture.
I lived in a Korean student dorm for a while, and the oldest girl in the dorm ran the dorm. She made all those students wake early in the morning, before classes, and clean their rooms and the bathroom, then stand at attention in the hallway while she made sure they did their jobs. After that, she took the all to chapel before they went on to class. They all had to go because she told them to, and they went happily. If the older student happened to be a drinker, they would be taking all the younger students out and forcing them to get drunk. It is just the way it works.
The grandparents are the ultimate in the hierarchy. On the holidays, everyone goes to their grandparents’ house, and they bow in front of their grandparents like the grandparents are kings and queens. You have to do what your grandparents tell you to do in Korea. You have no choice. Their will supersedes everyone’s will. If you don’t do what they say, they may physically force you to do it, and no one will hit them back because of their age. My daughter always loved her Korean father in law until she had an appointment one day, and he made another appointment he thought was better for her. He took her arm and forced her to go with him. She is American, and it made her mad, but she eventually forgave him. It was a normal thing for a Korean parent or parent in law to do. It doesn’t matter how old someone gets in Korea, they are still accountable to their parents. I have a good friend in his forties who is Korean. He is the father of four kids, but he still listens to his father as if he were a little boy and does everything his father tells him to do without question. It is just the way it is. My Korean son in law is the same way about his father. He thinks the sun rises and sets in his father and that he is the wisest man in the world. He does anything his dad tells him to do.
There is another factor to all this, the “ajuma.” An “ajuma” is a married woman who has kids. Often, they are grandmothers. The ajuma is known for being strong and forceful. If an ajuma is there, no one can argue with her. When that woman was young, she was extremely polite and did every everyone asked her to do, but she doesn’t do it anymore. She is everyone’s boss, and she knows it. People warned me from the beginning to look out for the ajumas. I have been in a grocery store standing at the shelves looking at what was there figuring out what I wanted to buy, and an ajuma came along and just pushed me out of the way physically and grabbed what she wanted. In my way of thinking, she was rude, but in her way of thinking, she was taking her right of being a strong old woman, an ajuma. The ajumas actually rule Korea, and some with an iron fist.
This is the Korean age system. With the older ones in charge, there is less crime, people can walk the streets at night without being afraid of being mugged. The basic morality of the people is higher. More people go to church or the Buddhist temple than in other countries. S. Korea is 50% Christian and 30% Buddhist. Those old people are doing their job at keeping the younger ones in line. No one is allowed in the public eye if they are known to be dishonest or immoral in any way. K-Pop stars are kicked out of the public eye if they are caught with illegal drugs, caught sleeping around, or caught drunk. Presidents are kicked out of office for having shady friends or end up killing themselves because they knew they did something wrong. The moral conscience of the Korean people is extremely high because the age system works. The whole country isn’t perfect, but they are working on it together.