Don’t know how they did the calculations here, but in Norway we have statistics for unemployment that goes down to 16 year olds.

However in those statistics, a person is only considered unemployed if they are not attending school. Our equivalent of high school is not mandatory, so a few people (very few) decide to quit school and begin working at 16. Some further people are high school dropouts that get jobs at 16-19.

So basically: You’re counted as unemployed if you’re not in a job or education.