You can buy it today. When I turned 21, I lived in California, where they carefully checked their ID cards. I went to a store, bought a bottle of gin and brushed it off. The employee said "Happy birthday" and called me!
For my 21st birthday, I like to sit at the bar and shop for energy drinks or some strawberry juice instead of alcohol. laugh out loud
You can buy it on your birthday. The number of people I've tagged coming to a bar I work for for their 21st birthday is too much.
Find a private driver and respect boundaries, knowing that kids love going to the beach.