As a more general thing for when you get there, I'd probably recommend going to EPCOT as your first park with him. It's probably the most Adult park at the world, and will give him a taste of Disney while not being overly kiddy it it's feel and offerings. Magic Kingdom while a great park, may have a more child-like feel for him with Fantasyland and the large numbers of animated characters featured within it.
Park wise, it'd probably be better to ease him into the Disney mindset by showing him what Disney is truly capable of in a more grown up place like EPCOT so he would be more appreciative of the Disney magic in the Magic Kingdom and able to look past the princesses and see what we all see as Disney for Adults.
(Hmmmm.... maybe also a breakfast at 1900 Park Faire before the Magic Kingdom day? Let the stepsisters drool over him and see what a Character interaction can be.

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