Does "nowi" mean "young" in addition to "new?" Using the word "new" to describe people is not all that common.
It may be used to describe eg. new student in class, or just like in the tv series New Girl - a roommate :) Meaning is close to English.
I can't think of any situation when you could say "nowi" for "young". Using "new" to describe people sounds a bit strange, but I believe it's put that way only to show the structure of the sentence. :)
I believe Duo uses odd constructions sometimes in order to teach us the limited vocabulary which has been introduced so far. It is difficult to construct natural sentences that utilize the entire dictionary if that dictionary is small.
Also in sentences like these you must rely less on context. This could be considered advantageous because it provides a greater challenge. Being able to recognize a word in a strange context can sometimes be useful. In the least, it makes you more aware of how firmly you have retained the word in your memory.