One comes to no good when young (3)
I believe the answer is:
you
'one' is the definition.
Both the definition and answer are singular nouns.
Maybe you can see an association between them that I can't see?
'no good when young' is the wordplay.
I cannot really see how this works, but
'no' could be 'o' (resembles 0 - 'no' can mean 'zero') and 'o' is found in the answer.
'young' could be 'y' and 'y' is found within the answer.
A single letter 'u' remains which might be clued in a way I don't see.
This may be the basis of clue (or it may be nonsense).
'comes to' is the link.
Can you help me to learn more?
(Other definitions for you that I've seen before include "Thee" , "My solvers in general" , "The audience as addressed by speaker" , "Reader" , "Personal pronoun" .)