Empty-headed happy youth (3)
I believe the answer is:
lad
'youth' is the definition.
(lad means a young man)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for lad that I've seen before include "Stable employee" , "Stable worker" , "A young chap into ballads" , "Shaver" , "Boy or youth" .)