Boast about French XI, first in Europe for a time (6,3)
I believe the answer is:
bronze age
'time' is the definition.
(historic period)
'boast about french xi first in europe' is the wordplay.
'boast' becomes 'brag' (synonyms).
'about' is an insertion indicator.
'french xi' becomes 'onze' ('eleven' in French).
'first in europe' becomes 'e' (1st letter of 'europe').
'brag' placed around 'onze' is 'bronzeag'.
'bronzeag'+'e'='BRONZE AGE'
'for a' is the link.
(Other definitions for bronze age that I've seen before include "Prehistoric period" , "remarkable culture" , "Archaeological period" , "Period of early history" , "Period between the Stone and Iron eras" .)