"Muchos adultos aquí son jóvenes."
Translation:Many adults here are young.
because duolingo is stressing that the adults are YOUNG where as you are stressing that many young adults are HERE.
It may not seem like much of a difference, but adjective placement is important. Adjectives generally live next to the noun they modify if that helps.
Muchos adultos aquí son jóvenes.= Many adults here are young. (Of the adults in this location, many are young. Stressing age.)
Muchos adultos jóvenes son aquí = Many young adults are here. (There are a lot of young adults at this place. Stressing location.)
The old cat is white. = El gato viejo es blanco.
The white cat is old. = El gato blanco es viejo.
This is especially important with words like "only" which can change the meaning of the sentence depending on where they're placed.
I want a new bike. (A simple statement of fact.).
Only 'I' want a new bike (no one else wants one).
I only 'want' a new bike (I don't want anything else).
I 'want' only a new bike (not a ball or a puppy... Though this is not traditional English phrasing).
I want only 'a new' bike (not an old bike).
I want a new 'bike' only (not a new bat or new ball).
I would say this as "Many adults are young here." The literal translation feels awkward.
Rachel it does mean young. In this sentence you are seeing tbe plural (..es) to agree with adultS, ok?
Didn't you read any of the comments that katevgrimes posted before yours? Everyone has the right to his own opinion, and I don't mind reading counterfactual arguments to a well-thought-out posting, but it wastes time, as well as taking up valuable real estate in the forum, when people have to wade through unsubstantiated personal opinions.