Youth is better.
They also accept "people" (so mixed gender), for "iuvenes" in some sentences and they'll accept it everywhere with report.
Gaffiot and Lewis really say that "iuvenis" is:
- a young person
- a young man
- a young woman
So, we have to report the "young woman" when it's not accepted.
In the latin sentence solus is the adjective. I would translate it as "The lonely young man does not live". But in the englisch sentence "alone" seems to describe how he lives (or in this case, how he does not live"). Isn't this an adverb? I'm not a native english speaker, maybe i understand it wrong.
First, your English (The lonely young man does not live) relates to ideas such as to live, to breathe, to not be dead. The common Latin verb for this is vivo, vivere, vixi, victum. However, Duo's sentence here involves a different Latin verb (habito, habitare, habitavi, habitatum), which is about residency or where a person sleeps and eats and returns at the end of normal days. Second, Duo is certainly describing the young man, the subject that requires the nominative case. In this sentence, the young man is described as not by himself, not alone, not without company, or not lonely. Third, and forgive me if this is clear already, the English word lonely does end in -ly but it is still an adjective.