How Old Are You Really?
My youngest son was born on 31 December 2009. Ask most of the world how old he is today and the answer is sixteen. Ask by the traditional Korean method and he’s eighteen. There’s a third method that makes him seventeen. He’d tell you he’s old enough to borrow the car, which is a fourth system entirely.
The sixteen is what most of us call age: the number of birthdays you’ve had, starting at zero. It’s often called “international age”.
The eighteen is traditional Korean age, which comes from an older East Asian way of counting. You’re one year old on the day you’re born, and everybody adds a year together on 1 January. So a baby born on New Year’s Eve turns two the very next day, which must make for an exhausting first week. The usual explanation is that you’re counting the calendar years someone has lived in, so the year you’re born is your first, and you can’t be in your first year and also be zero.
The seventeen is “year age”, which splits the difference. You start at zero, like the rest of the world, but everyone still adds a year on 1 January, so your age is simply this year minus the year you were born.
For a long time, all three ran side by side in South Korea, which caused exactly the confusion you’d expect: in contracts, in medical advice, in deciding when people became eligible for things. So in June 2023, the government made international age the standard for legal and administrative purposes. Year age still survives in a few specific laws, and Korean age is still part of everyday conversation for plenty of people, because a law can change paperwork far faster than it can change habit.
What I like about all this is that English does the same thing and nobody notices. We say a baby is “in their first year” and also “zero years old”, and never feel the contradiction. We call the 1900s the twentieth century. Ordinal numbers, first and second and third, count which year you’re in. Cardinal numbers, one and two and three, count how many you’ve finished. Korean age simply chose the ordinal.
Which is a useful reminder that numbers aren’t as objective as they look. Every number is the output of a counting rule, and the rule is usually invisible. Australia’s financial year runs from July to June, so “this year’s results” means something different in Melbourne than in New York. “Year to date” depends on when your year starts. Two departments can report different headcounts and both be right, because one counts part-timers and the other doesn’t.
Most of the arguments I’ve seen in organisations about whose figures are correct are really arguments about which counting rule each side was using without saying so. The numbers get debated, the rules never do, and everyone leaves convinced the other side can’t add up.
So when a number matters, ask how it was counted before you ask whether it’s right. You might find, like my son, that it’s perfectly possible to be three different ages at once, and that the interesting question is never which one is true, but who decided how we’d count.
