Of a certain age, one Dotty settled here in Rome (9)
I believe the answer is:
neolithic
'of a certain age' is the definition.
(relating to the later part of the Stone Age)
'one dotty settled here in rome' is the wordplay.
'dotty' is an anagram indicator.
'settled' becomes 'lit' (I've seen this in another clue).
'here in rome' becomes 'hic' ('here' in Latin).
'one' with letters rearranged gives 'neo'.
'neo'+'lit'+'hic'='NEOLITHIC'
(Other definitions for neolithic that I've seen before include "Description of ancient people" , "about when stone weapons prevailed" , "Belonging to late Stone Age" , "Relating to the later Stone Age" , "Of New Stone Age" .)