Hello Andrew,
Your dear son sounds just like my kind of dining pal because some of my most favourite Disney restaurants are exactly as you describe - not too adult, but not too child and I especially love Sci-Fi Dine-In Theater Restaurant!
Here in no particular order is a list just for you of some delicious dining suggestions -
For a really cool culinary experience try
50's Prime Time Cafe, but be sure mind your manners!
Dine on the wild side at
Sanaa where you might just see animals native to the African savanna roaming outside your window.
Check out the Oompa Band at the
Biergarten Restaurant where it's Oktoberfest every day.
Definitely try the Grey Stuff at
Be Our Guest Restaurant; it's delicious, don't believe me? Just ask the dishes!
Diners at the
Whispering Canyon Cafe enjoy an absolute hoot! Be sure to ask for ketchup or straws.
I'm sure where ever is finally decided you'll enjoy a magical trip to Walt Disney World Resort making memories with your lovely son which will last for an entire lifetime.
Also, I thought you may find this
Services for Guests with Cognitive Disabilities link to be a useful planning resource.
Have a great Disney day.
~ Jane