Hi Robert,
Thank you for visiting the Disney Parks Moms Panel with your question!
My guess is that your 7-year-old will be able to ride on most attractions. At Walt Disney World, restrictions on attractions are done by height rather than age. While there are some
attractions with height requirements, most do not have height requirements. The Disney Parks Blog post that I just linked to has a chart with height requirements for attractions at Magic Kingdom, and links to height requirements for attractions at Epcot, Disney's Hollywood Studios, and Disney's Animal Kingdom.
Attractions with the tallest height requirements include Rock 'n' Roller Coaster at Disney's Hollywood Studios and Primeval Whirl at Disney's Animal Kingdom, both of which have a 48 inch height requirement; and Space Mountain at Magic Kingdom, as well as Expedition Everest and Avatar Flight of Passage at Disney's Animal Kingdom, all of which have a 44 inch height requirement.
You can also find the height requirement for attractions on the attraction pages themselves. For example,
Big Thunder Mountain Railroad at Magic Kingdom has a height requirement of 40 inches, which you find in the information at the upper right side of the webpage.
Of course, you do have to consider what your child prefers in a ride experience. Even if your child meets the height requirement, you know your child best, so consider preferences. Some children do not want to go on thrilling attractions, and there are plenty of other options if they do not want to do these more thrilling experiences!
I hope that these thoughts are helpful for you, Robert. Please do let us know if you have any further questions!