In essence first character goes back to the previous season (6)
I believe the answer is:
mature
'season' is the definition.
(thesaurus)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for mature that I've seen before include "Fully grown and developed (6)" , "due to be paid" , "sensible" , "reach the end of term" , "Old film star" .)