Kaycey, thank you for the opportunity to pretend I'm 21 all over again. Truth be told, I got shorted one hour of celebration time due to clocks (at respectable establishments) preemptively "springing forward" for daylight savings time on the night of my 21st birthday.
I'd recommend staying somewhere on the BoardWalk. You can walk to Epcot, and you have the best options to extend the evening at your doorstep. Start at Epcot mid-afternoon with a tequila flight at Cava del Tequila. Then, get a little crazy and take on some mezcal. You're only young once, right?
Proceed to Germany for a reservation at Biergarten for dinner. Get a litre or two of beer (doppelbock, if it's on tap) and enjoy the bounty of buffet items to soak up the mezcal and keep you full for the night ahead. After dinner, keep swinging clockwise around World Showcase. Make sure to stop in Japan at the Kaki Gori food cart for some sake and plum wine. France has two must dos: the Grey Goose lemonade slushy and the Grand Marnier slushy. You might be best served by taking a pause between the two slushies and enjoying a sweet treat or two from Boulangerie Patisserie.
If you still have a spring in your step, make your way over to
Jellyrolls on the BoardWalk to end the night.
Happy birthday to you.