Hello and welcome!
I'm unsure if you're wanting information regarding character performer dancers (in shows/parades) or the professional equity dancers who are hired based on contracts and only do such shows as Dream Along With Mickey or Beauty and the Beast.
If you're speaking of character performers, I believe I can answer some of your questions as that's where my background lies.
1) I believe Disney hires anyone 16 and older, answering your next question...
2) You don't need any specific education to get hired. It's based on a successful audition and what they need currently.
3) Current entertainment cast members actually have their own physical trainers for each show/parade, so they are given exercises/warmups at the beginning each shift. These typically are basic warmups getting different muscle groups active and moving in order to avoid injuries to performers.
I say go into the audition and have fun with it! Don't be stressed; show them how excited you are to be there, through your smile and energy. If you mess up something, keep going and don't be frustrated with yourself. There will be hundreds of people there, so just expect that and make sure you make yourself stand out in some way.
Last, but not least, Break a leg!!
