Near ancient doddery oldster (11)
I believe the answer is:
centenarian
'oldster' is the definition.
(centenarian is a kind of oldster)
'near ancient doddery' is the wordplay.
'doddery' is an anagram indicator.
'near'+'ancient'='nearancient'
'nearancient' is an anagram of 'CENTENARIAN'.
(Other definitions for centenarian that I've seen before include "Person of a great age" , "Person a hundred or more in age" , "old human being" .)