Oldster entering northbound metro in Essen (6)
I believe the answer is:
senior
'oldster' is the definition.
'entering northbound metro in essen' is the wordplay.
'northbound' is a reversal indicator.
'entering' indicates a hidden word.
'roines' is hidden within 'metro in essen'.
'roines' back-to-front is 'SENIOR'.
(Other definitions for senior that I've seen before include "Higher in status" , "Elder (of two)" , "High-ranking" , "More advanced in years or authority" , "Higher in rank or age" .)