Foreigners living in Korea quickly learn that the Korean way of counting age is different. When you are young, it is great as you appear older, more mature. As you age, the appeal declines commensurately.
Many explanations have been put forward. "We count the time in the womb" is a common one. However, this barely scratches the surface. It fails to explain why someone born in December is a full year older than the person born in January.
Time in the west measures duration – be it years, months, days or hours. In Korea, time marks time periods. 7 years old means 'in the seventh year'. Three days really means 'on the third day'. (It will be ready in 3 days actually means it will be ready the day after tomorrow.)
When recognize that the peg is actually square, we will be less frustrated when we find ourselves trying to fit it into the round hole.