"Sam is new."
I'm new at Arabic, so for all I know you are correct. But how do you know this word for "new" (an adjective) means "young," which can be a noun? There seem to be several words in Arabic for young, including شاب. A.S. Tritton (Arabic [Teach Yourself Books] 1943) p. 31 gives new as جديد, but one of the words for young in the sense of "youth" is حداثة (p. 211). I don't even have a dictionary, so maybe your dictionary gives both new and young for جديد?