Rep theatre in London, years earlier (5)

I believe the answer is:
agent
'rep' is the definition.
(I've seen this before)
'theatre in london years earlier' is the wordplay.
I cannot quite see how this works, but
'theatre' could be 'nt' (National Theatre) and 'nt' is found in the answer.
'years' could be 'age' (period of many years) and 'age' is present in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for agent that I've seen before include "One's representative" , "One employed to incite others to commit illegal acts" , "He or she acts for actors" , "Catalyst" , "Dealer" .)
