Hi Sammy,
How fun to be planning a first trip to Walt Disney World! There are so many wonderful restaurants at
Walt Disney World that accept reservations. Since you are planning a special celebration, I do suggest that you choose a restaurant that accepts reservations so that you can be sure to dine when and where you would like to. Let me offer you a few of my favorites for a special celebration.
California Grill is a modern location serving California cuisine. The location is atop Disney's Contemporary Resort, so the view is amazing. If you time it right, you can even watch the fireworks at Magic Kingdom from this unique viewpoint - there are even outside spaces from which to watch the fireworks! If your birthday teenager loves steak, give
Yachtsman Steakhouse a try. This steakhouse offers delicious steak and seafood in a lovely setting at Disney's Yacht Club Resort. If your family is up for something a little more adventurous, consider
Jiko - The Cooking Place. This restaurant is located at Disney's Animal Kingdom Lodge and offers upscale dining with flavors from Africa. After a meal here, you can go see animals on the savanna at the resort.
Those are just a few of my favorites, Sammy. I suggest that you take a look at the list of restaurants I linked early in this answer to see what appeals to you. In order to make reservations at the restaurant you choose, you can either use the restaurant's website, or call 407-WDW-DINE (407-939-3463).
Please do let us know if you have any further questions, Sammy!