Old-fashioned athlete, a carriage attendant once (9)
I believe the answer is:
outrunner
'a carriage attendant once' is the definition.
(attendant running beside a carriage)
'old-fashioned athlete' is the wordplay.
'old-fashioned' becomes 'out' (as opposed to 'in').
'athlete' becomes 'runner' (type of athlete).
'out'+'runner'='OUTRUNNER'
(Other definitions for outrunner that I've seen before include "leading dog" , "One goes faster than" , "one that covers even more ground" , "dog lead?" .)