He's young to go around being bossy! (3)
I believe the answer is:
boy
'he's young to go around being bossy' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'he's young' is the wordplay.
'he' becomes 'bo' ().
'young' becomes 'y'.
'bo'+'y'='BOY'
Can you help me to learn more?
(Other definitions for boy that I've seen before include "Youth" , "Young male" , "Youthful male" , "Male child" , "Lad" .)