Old-fashioned sort of climbing gear, half gone mouldy, ultimately (5)
I believe the answer is:
fogey
'old-fashioned sort' is the definition.
(as in an old fogey)
'of climbing gear half gone mouldy ultimately' is the wordplay.
'climbing' shows that the letters should be reversed in order (in a down clue, letters climb up).
'half gone' suggests halving the letters.
'ultimately' says to take the final letters.
The last letter of 'mouldy' is 'y'.
'of' written backwards gives 'fo'.
'gear' halved is 'ge'.
'fo'+'ge'+'y'='FOGEY'
(Other definitions for fogey that I've seen before include "Fussy, old-fashioned person" , "Old stick-in-the-mud" , "Old-fashioned type" .)