Age 100 appearing in A New Hope (5)
I believe the answer is:
epoch
'age' is the definition.
(thesaurus)
'100 appearing in a new hope' is the wordplay.
'100' becomes 'c' (roman numeral).
'appearing in' indicates putting letters inside.
'a new' indicates anagramming the letters.
'hope' with letters rearranged gives 'epoh'.
'c' put within 'epoh' is 'EPOCH'.
(Other definitions for epoch that I've seen before include "Particular historic time period" , "Period of time in history" , "Significant period" , "years" , "Major division or period of history" .)