> South Koreans will become at least a year younger...
"At least"?
Who is becoming two years younger...?
"At least"?
Who is becoming two years younger...?
Under the old system you were one year old at birth, and a year older at the beginning of the next year (not, as one might expect, at their next birth day.) That means at the beginning of the year on which under the more common system one would be not-yet-one, a person under the Korean system would be two (unless they were born on the first day of the year, when they would be only one.)
I can't imaging that it's particular practical to think of some one who has only been alive for a few days as being two years old. It's not even useful if you think of it as the child being "in their second year". Technically true, but what are you trying to convey?
The number of winters you survived probably.
Folk descriptions of age in my corner of the world often used springs as a unit - to this day the plural form for years in my language(Polish) reads as "summers".
If school starts a six, then some of those children could be one to two years younger than others. For adult either way seems fine, there's little difference between 35 and 37, but for the youngest children it seems like it would make a huge difference.
An infant born on 2022-01-01 is currently "2", the same "age" as a baby born on 2022-12-31.
A Korean born on, say, 2001 December 1st would have been one year old in 2001, two years old in 2002, and 23 years old today, based on the traditional counting. In Western counting, the person would be 21 years old today.