Age creeps up for retirement, one admitted (6)
I believe the answer is:
season
'age' is the definition.
(thesaurus)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for season that I've seen before include "Particular time (for activity, conditions etc)" , "Flavour food with salt, pepper etc" , "Salt, maybe" , "Add flavour at a certain time of year" , "Spring, say" .)