Mawkish agent embraces old people at first (5)
I believe the answer is:
soppy
'mawkish' is the definition.
(I've seen this in another clue)
'agent embraces old people at first' is the wordplay.
'agent' becomes 'spy' (spy is a kind of agent).
'embraces' indicates putting letters inside.
'at first' suggests taking the first letters.
The first letters of 'old people' is 'op'.
'spy' enclosing 'op' is 'SOPPY'.
(Other definitions for soppy that I've seen before include "Daft" , "Indulgently sentimental" , "Mushy" , "Emotional" , "Informally sentimental in sickly way" .)