Very excited (4)
I think it could be either:
'very excited' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for agog that I've seen before include "Very eager (to hear/see)" , "Highly excited in anticipation" , "Unable to wait" , "Interested, excited and eager to know more" , "Eagerly awaiting" .)
(Other definitions for gaga that I've seen before include "Slightly mad (colloq.)" , "Very fond of" , "Barmy joke, third in cracker" , "crackers" , "Slangily crazy, off one's head" .)