Old man in Derby gear, getting dressed up (9)
I believe the answer is:
greybeard
'old man' is the definition.
(I know that old man can be written as greybeard)
'derby gear getting dressed up' is the wordplay.
'getting' means one lot of letters go next to another.
'dressed up' indicates anagramming the letters.
'derby'+'gear'='derbygear'
'derbygear' anagrammed gives 'GREYBEARD'.
'in' is the link.
(Other definitions for greybeard that I've seen before include "Sage" , "Old man" .)