Stage one perhaps in the development of civilisation (5,3)
I believe the answer is:
stone age
'development of civilisation' is the definition.
The definition suggests a singular noun which matches the answer.
'stage one perhaps' is the wordplay.
'perhaps' is an anagram indicator.
'stage'+'one'='stageone'
'stageone' anagrammed gives 'STONE-AGE'.
'in the' acts as a link.
Can you help me to learn more?
(Other definitions for stone age that I've seen before include "25 [ERA]" , "Early period" , "Go, senate to ancient era before metal was discovered" , "Pre-historic era" , "Neolithic" .)