Invented age held in high regard (9)
I believe the answer is:
venerated
'invented' is the definition.
Both the answer and definition are adjectives. Maybe they are linked in a way I don't understand?
'age held in high regard' is the wordplay.
'age' becomes 'era' (both can mean a long time).
'held in' is an insertion indicator.
'high regard' becomes 'vented' (I can't justify this - if you can you should give a lot more credence to this answer).
'era' going within 'vented' is 'VENERATED'.
Can you help me to learn more?
(Another definition for venerated that I've seen is " Revered, hallowed".)