Age stomach's beginning to go from drinking a lot (6)
I believe the answer is:
thirty
'age' is the definition.
(thirty years old)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for thirty that I've seen before include "Half of threescore" , "Number of pieces of silver paid to Judas" , "Sum of first four perfect squares" , "Days in September, April, June and November" , "Roman number XXX" .)