Louisiana drinking age bounced back and forth for a while. There are lots of places here that are VERY lax about carding.LSA R.S. 93:13 makes it illegal for anyone to buy alcoholic beverages for anyone under the age of 21 years except for a parent, guardian or spouse of the person under 21.
So, it would appear that someone under 21 years cannot buy or have in his possession (in public) any alcoholic beverage. It would also appear that it would not be illegal for someone under 21 to drink at home if a parent buys the booze.