The years of immaturity, say, soon will be over (6)
I believe the answer is:
nonage
'be over' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'the years of immaturity say soon' is the wordplay.
I cannot quite understand how this works, but
'years' could be 'age' (period of many years) and 'age' is present in the answer.
'of' could be 'o' and 'o' is found within the answer.
This explanation may well be incorrect...
'will' acts as a link.
Can you help me to learn more?
(Other definitions for nonage that I've seen before include "(Legal) infancy" , "State of being unable to marry" , "Period of youth before maturity" , "Years before adulthood" , "Period of immaturity" .)