Not as old as old French article with odd grey exterior (7)
I believe the answer is:
younger
'not as old' is the definition.
('young' can be the opposite of 'old' so perhaps 'younger' is reasonable for 'not as old')
'old french article with odd grey exterior' is the wordplay.
'old' becomes 'o' (abbreviation as in OT - Old Testament).
'french article' becomes 'un' (indefinite article in French).
'with' says to put letters next to each other.
'odd' is an anagram indicator.
'exterior' indicates putting letters inside (some letters go on the outside of others).
'grey' anagrammed gives 'yger'.
'o'+'un'='oun'
'oun' going into 'yger' is 'YOUNGER'.
'as' is the link.
(Other definitions for younger that I've seen before include "Comparatively raw" , "Less grey" , "more boyish" , "Seven PM" , "Less experienced" .)