To a youngster, it means a little extra (3-2)
I believe the answer is:
top-up
'to a youngster it means a little extra' is the definition.
I can't judge whether this definition defines the answer.
'to a youngster' is the wordplay.
'a youngster' becomes 'pup' (a pup is a young dog).
'to'+'pup'='TOP-UP'
Can you help me to learn more?
(Other definitions for top-up that I've seen before include "Extra addition" , "Additional amount to restore mobile phone credit, for example" , "Supplement" , "Amount required to restore something's level" , "Replenished drink" .)