That is not true for most states in Germany.

After 10 years of mandatory school most states have what is called "Berufsschulpflicht" until you are at least 18 years old.

That means you have to learn a job, which is not the same as working full-time and still considered education.

16 year olds in Germany are employed and they can work 40 hours a week.

Claiming that 16 year olds "can not work because they have mandatory school" is false.