Leader of Mysterons probes couples for ages (5)
I believe the answer is:
times
'ages' is the definition.
(I've seen this before)
'leader of mysterons probes couples' is the wordplay.
'leader of' suggests taking the first letters.
'probes' indicates putting letters inside (probe can mean to poke or prod into).
'couples' becomes 'ties' (couple can mean to link or tie).
The first letter of 'mysterons' is 'm'.
'm' placed inside 'ties' is 'TIMES'.
'for' acts as a link.
(Other definitions for times that I've seen before include "Paces" , "operator" , "measures the length of something" , "Big Apple's theatre district" , "See 1" .)