Time I had to accept I’m retiring (5)
I believe the answer is:
timid
'retiring' is the definition.
(I've seen this in another clue)
'time i had to accept i'm' is the wordplay.
'time' becomes 't' (abbreviation).
'i had' becomes 'i'd' (contraction).
'to accept' means one lot of letters goes inside another.
'i'm' becomes 'mi' (I can't explain this - if you can you should give a lot more credence to this answer).
'id' placed around 'mi' is 'imid'.
't'+'imid'='TIMID'
(Other definitions for timid that I've seen before include "Lacking in confidence" , "Easily alarmed, shy" , "Inclined to avoid people" , "not forward" , "Easily scared" .)