Extremely sweet, old, grey and boring (6)
I believe the answer is:
stodgy
'boring' is the definition.
(I've seen this before)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for stodgy that I've seen before include "not easily assimilated" , "(Of food) solid and heavy" , "Heavy to eat" , "(Of food) heavy, rich" , "Heavy, starchy and hard to digest" .)