"Das Medium ist so alt."
"Das Medium ist so alt." makes perfect sense but not as you would think.
"Das Medium" would be understood as "the psychic". So we are talking of an old psychic here.
Because of that, "Medium" is ambiguous in German and it is seldom used in the singular form for "medium". You could use it in the plural and in compound forms "Nachrichtenmedium" "Unterhaltungsmedien". In the intended sense, you could say: "Zeitungen sind so ein altes Nachrichtenmedium."