Hi Jacqueline! That is awesome that you want to do this for your birthday! It is also an anniversary for the
Disney World Marathon. It will be the 20th year, so the marathon has been around longer than you!
The marathon will be 26.2 miles long and will wind throughout the Disney World property (including through all four parks!). You do not have to run the whole time. In fact, a lot of people don't. I do what is called the run/walk/run method of training. It was developed by
Disney's official trainer, Jeff Galloway. You will run for an interval, then walk for an interval, repeating it throughout the race. Definitely check out that link above to the Jeff Galloway method on Disney's website. He will even create a customized marathon training program for the 2013 Disney marathon. You do have to maintain an overall pace of a 16 minute/mile for the race.
You can expect a lot of things for the Disney marathon. Many people wear costumes, there will be runners of ALL levels, and some people will speed-walk the entire race. There will also be a lot of inspirational runners. The race course is filled with Disney magic like character greetings, videos, music, fireworks, and much more. RunDisney races are so much more than just a race. It is more of an awesome adventure!
I hope this helps you! Please feel free to send me any more questions you may have about runDisney! I hope to see you at the marathon in January!!