"Are you young?"
Translation:Ti fiatalok vagytok?
You only omit "van" in third person, never in second, so the correct sentence is: "Te fiatal vagy?"
Fair enough, but just now when I entered "te fiatal?" (incorrect, as you say), the correct translation given was "Ön fiatal?", which seems to violate your rule. Can you clarify?
I put "Vagy fiatal." and it gave me "Maga fiatal." What does that mean and why?