Starts to believe, expecting very young group (4)
I believe the answer is:
bevy
'group' is the definition.
The answer is an example.
'starts to believe expecting very young' is the wordplay.
'starts to' indicates taking the first letters.
The initial letters of 'believe expecting very young' is 'BEVY'.
(Other definitions for bevy that I've seen before include "What's sold at number 3 [WATERING HOLE]" , "Flock; alcoholic drink" , "female company?" , "Group (of larks, ladies etc)" , "Gaggle" .)