Strait-laced English woman, very old (8)
I believe the answer is:
primeval
'very old' is the definition.
(primeval means ancient or very old)
'strait-laced english woman' is the wordplay.
'strait-laced' becomes 'prim' (synonyms).
'english' becomes 'e' (abbreviation).
'woman' becomes 'Val' (val is a name for a woman).
'prim'+'e'+'val'='PRIMEVAL'
(Other definitions for primeval that I've seen before include "From the earliest times" , "having come first in history" , "Ancient" , "Prehistoric" , "Instinctive" .)