Gaped at last, grey bearded (6)
I believe the answer is:
yawned
'gaped' is the definition.
('yawn' can be a synonym of 'gape')
'last grey bearded' is the wordplay.
'last' indicates one should take the final letters.
'bearded' becomes 'awned' ('awned' can be similar in meaning to 'bearded').
The last letter of 'grey' is 'y'.
'y'+'awned'='YAWNED'
'at' acts as a link.
(Other definitions for yawned that I've seen before include "Showed signs of tiredness" , "Gave mute evidence of boredom" , "Opened mouth wide as expression of boredom" , "Showed that one was tired" , "Gaped, wide open" .)