He hasn't yet made a score (8)
I believe the answer is:
teenager
'he hasn't yet made a score' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
This is the entire clue.
Can you help me to learn more?
(Other definitions for teenager that I've seen before include "one that's not yet made a score?" , "Old child or young adult?" , "Generate (anag)" , "14, perhaps" , "Youngster" .)