An indication of assent over car's current age (4,6)
I believe the answer is:
anno domini
'current age' is the definition.
(as opposed to 'Before Christ')
'an indication of assent over car's' is the wordplay.
'indication of assent' becomes 'nod' (a nod indicates agreement).
'over' becomes 'o' (cricket abbreviation).
'car' becomes 'mini' (Mini Cooper).
'an'+'nod'+'o'+'mini'='ANNO DOMINI'
(Other definitions for anno domini that I've seen before include "later days" , "having a date, she may put it on" , "Advancing old age (informal)" , "In the year of our Lord" , "AD in full" .)