Is he young to be in uniform? (5)
I believe the answer is:
cadet
'is he young to be in uniform?' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'is he' is the wordplay.
I cannot really see how this works, but
'he' could be 'cad' and 'cad' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for cadet that I've seen before include "young soldier" , "Trainee -- acted (anag)" , "Junior officer; younger brother" , "Officer-trainee" , "Police or armed forces trainee" .)