Translation:That man is still young.
Exactly! Guy is used so often. Of course, where I'm from, guys means men and women.
This is incorrect because ano is directly modifying otoko. They go together and so must be translated together as that man.
Written English tends to place emphasis on the last word of the sentence: "that is still a young man" places emphasis on man (as opposed to woman), whereas "that man is still young" places emphasis on young (as opposed to old). If you were speaking or had formatting control, you could change your tone or use italics to emphasize different parts of the sentence and get opposite meanings, but let's keep it simple and formal for now.
But, in this sentence "ano" is a modifier, not a pronoun. "Is still young" is a comment on "that man (as opposed to any other man). It is not a definition of "that".
How can you tell that まだ here is "still" & not "not yet"? (Other than because "not yet" wouldn't make much sense?)