Usually working, say, with maturity (2,7)
I believe the answer is:
on average
'usually' is the definition.
(I've seen this before)
'working say with maturity' is the wordplay.
'working' becomes 'on' (on can mean working or activated).
'say' becomes 'aver' (synonyms).
'with' means one lot of letters go next to another.
'maturity' becomes 'age' (I've seen this before).
'on'+'aver'+'age'='ON AVERAGE'
(Other definitions for on average that I've seen before include "Generally" , "Usually" , "typically speaking" .)