Stage of culture one runs on maturity (4,3)
I believe the answer is:
iron age
'stage of culture' is the definition.
The definition and answer can be both related to time as well as being singular nouns.
Perhaps you can see a link between them that I can't see?
'one runs on maturity' is the wordplay.
'one' becomes 'I' (Roman numeral).
'runs' becomes 'r' (cricket abbreviation).
'maturity' becomes 'age' (I've seen this before).
'i'+'r'+'on'+'age'='IRON AGE'
Can you help me to learn more?
(Other definitions for iron age that I've seen before include "Time of the spread of metal weapons, tools etc" , "Prehistoric period" , "Ancient period in the development of mankind" , "A region (anag) - period long ago" , "Period in the history of man - a region (anag)" .)