Hi Danielle,
I brought my brother to Walt Disney World as a birthday gift once. It was so much fun! The first thing that I suggest, and that I did for my brother, was to get him a birthday button. These are free at Guest Relations at any of the theme parks. It was great to hear cast members and guest wishing my adult brother a happy birthday all day long at Walt Disney World when they saw his button!
You mention that your brother is a big Mickey Mouse fan. I suggest that you take a look at the gifts available from
Disney Floral and Gifts. You can search under "Characters and Themes" to find gifts that include Mickey Mouse. Likewise, explore the options of having a Mickey Mouse cake or other custom cake made for your brother. You could even order him special Mickey Mouse birthday ears! You can explore these options at the
Disney Customize Your Special Occasion web page.
Finally, on his birthday, why not book a character meal where he can meet Mickey Mouse? Consider Chef Mickey's in Disney's Contemporary Resort. For a more out of the way, but really fun experience, try
Mickey's Backyard BBQ for foot-stomping fun and good food! Please note that character appearances are subject to change.
I hope that this gives you some ideas for your brother's birthday, Danielle. Have a great time planning, and please do not hesitate to ask if you have any further questions.