"He writes about our age."
Translation:Hij schrijft over onze leeftijd.
As a native dutch speaker this sentence makes no sense whatsoever: why would anybody write about "our age" meaning how old you are. I have never heard in dutch "hij schrijft over onze leeftijd". It is far more plausible to write about "our age" meaning about the era we live in. In dutch it would also make a lot more sense: "hij schrijft over onze eeuw (de eeuw waarin wij leven)". Technically it is possible to translate the sentence the way DL wants us to, but it makes no sense. The course is supposed to teach you common basic dutch and the DL translation is far from conversational dutch.