Score century finally, after time passed (6)
I believe the answer is:
twenty
'score' is the definition.
('twenty' can be a synonym of 'score')
'century finally after time passed' is the wordplay.
'finally' indicates one should take the final letters.
'after' means one lot of letters go next to another.
'time' becomes 't'.
'passed' becomes 'went' (I've seen this in other clues**).
The final letter of 'century' is 'y'.
't'+'went'='twent'
'y' after 'twent' is 'TWENTY'.
(Other definitions for twenty that I've seen before include "Dozen plus eight" , "John B Keane wrote about many young men of this age" , "This twice denotes normal vision" , "No. between 5 and 1 on dartboard" , "Number" .)