Grey, perhaps, almost before one's time (4)
I believe the answer is:
earl
'one's time' is the definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.
'grey perhaps almost before' is the wordplay.
'grey perhaps' becomes 'wear' (grey is a kind of wear).
'almost' means to remove the first letter.
'before' becomes 'l' (I can't justify this - if you can you should believe this answer much more).
'wear' with its first letter taken off is 'ear'.
'ear'+'l'='EARL'
Can you help me to learn more?
(Other definitions for earl that I've seen before include "Essex, say" , "Male member of British nobility" , "Lear (anag)" , "Noble title" , "Countess his wife" .)