Linking a tiny disorder with middle age (5)
I believe the answer is:
tying
'linking' is the definition.
(tying is a kind of linking)
'a tiny disorder with middle age' is the wordplay.
'disorder with' indicates an anagram (I've seen 'diseased' mean this (I've seen this in other clues)).
'middle' indicates the central letters.
The centre of 'age' is 'g'.
'tiny' anagrammed with 'g' can make 'TYING'.
(Other definitions for tying that I've seen before include "Restricting" , "Binding, fastening" , "restrictive" , "Scoring the same" , "lacing" .)