Old judge to make a speech (5)
I believe the answer is:
orate
'make a speech' is the definition.
(I've seen this in another clue)
'old judge' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'judge' becomes 'rate' (rating is a kind of judging).
'o'+'rate'='ORATE'
'to' acts as a link.
(Other definitions for orate that I've seen before include "Deliver a speech" , "Erato (anag.)" , "Spout" , "Make a formal speech" , "Speak pompously and at length" .)