This is the 3431st most frequent Dutch word.
middelbare
"Secondary" (relating to middle/high school level).
Here, 'middelbare' refers to the age or level of the school within the context of the Dutch education system, translating to 'secondary' in English.
Hij zit op de middelbare school.
He attends secondary school.
Here, 'middelbare' is used to describe 'leeftijd' ('age'), meaning 'middle' or 'moderate,' referring to the age range in context.
Voor middelbare leeftijd is hij nog vrij actief.
For middle age, he is still quite active.
Again, 'middelbare' refers to the educational level deemed appropriate for the mentioned age group.