Old and long, say (5)
I believe the answer is:
opine
'say' is the definition.
(I've seen this before)
'old and long' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'and' is a charade indicator (letters next to each other).
'long' becomes 'pine' (to pine for someone is to long for them).
'o'+'pine'='OPINE'
(Other definitions for opine that I've seen before include "Suggest" , "Think - express a view" , "Express one's view" , "State as one's opinion" , "Believe" .)