Mawkish agent embraces old people at first (5)
I believe the answer is:
soppy
'mawkish' is the definition.
(I know that mawkish can be written as soppy)
'agent embraces old people at first' is the wordplay.
'agent' becomes 'spy' (spy is a kind of agent).
'embraces' means one lot of letters goes inside another.
'at first' says to take the initial letters.
The initial letters of 'old people' is 'op'.
'spy' going around 'op' is 'SOPPY'.
(Other definitions for soppy that I've seen before include "Daft" , "Indulgently sentimental" , "Mushy" , "Emotional" , "Informally sentimental in sickly way" .)