Short answers, pulled from the story.
The word gymnasium derives from the Ancient Greek term gymnasion, meaning a place for physical training. In ancient Athens, teachers gathered between hours of exercise to instruct young men in intellectual matters.
Prussian regulations in 1812 officially mandated that all schools sending students to universities must bear the name gymnasium. This standardization spread through the Austrian-Hungarian, German, and Russian Empires by the 20th century.
Students entering gymnasiums typically range between ages 10 and 13 after being selected from general populations. Core subjects include literature, mathematics, informatics, physics, chemistry, biology, geography, art, music, history, philosophy, civics, social sciences, and foreign languages.
Denmark, Estonia, Finland, Iceland, Latvia, Norway, Sweden, and the Faroe Islands structure their gymnasiums around three-year programs starting when students turn sixteen after nine or ten years of primary school.
The duration varies between six and seven years in Berlin and Brandenburg but reaches eight years in Bavaria, Hesse, and Baden-Württemberg. Saxony and Thuringia limit instruction to eight years maximum.