I don't think there is any legal age for the whole country as a whole.. It ranges from 18 - 25 from what I know with restrictions on its consumption in some NE States and Gujrat..U r landing in Ahmedabad, which since in Gujrat may hv strict rules for this..
Maybe fellow Fter's can give more info on this, but wasnt Gujrat supposed to be a alcohol free state, where offically we were not allowed to even carry alcohol ? Please correct me if I am wrong..
But am sure that the min age is not fixed but ranges as mentioned above..