Valley seeing return of English youth (4)
I believe the answer is:
dale
'valley' is the definition.
(I know that Dale is a type of valley)
'return of english youth' is the wordplay.
'return of' is a reversal indicator.
'english' becomes 'E' (abbreviation as in OED).
'youth' becomes 'lad' (lad means a young man).
'e'+'lad'='elad'
'elad' backwards is 'DALE'.
'seeing' acts as a link.
(Other definitions for dale that I've seen before include "Valley, particularly in Northern England" , "Low ground" , "Valley; man's name" , "See 8" , "depression" .)