Youngster lurking around on a regular basis (4)
I believe the answer is:
girl
'youngster' is the definition.
'lurking around on a regular basis' is the wordplay.
'lurking' becomes 'lollygaging' ('lollygag' can be a synonym of 'lurk').
'around' indicates the central letters.
'on a regular basis' becomes 'irl' (I am not sure about this - if you are sure you should believe this answer much more).
The middle letter of 'lollygaging' is 'g'.
'g'+'irl'='GIRL'
Can you help me to learn more?
(Other definitions for girl that I've seen before include "See 5" , "Lassie" , "One of 8 [LASSES]" , "A young female" , "Lass" .)