It's after wild fun that you're not in good shape (5)
I believe the answer is:
unfit
'not in good shape' is the definition.
(I've seen this before)
'it's after wild fun' is the wordplay.
'after' says to put letters next to each other.
'wild' indicates an anagram.
'fun' is an anagram of 'unf'.
'it' after 'unf' is 'UNFIT'.
'that you're' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for unfit that I've seen before include "Ill - out of shape" , "Incapable" , "Incompetent" , "not worthy" , "Not in good physical shape (5)" .)