Disney has had a long-standing policy that prohibits adult costumes. If an adult dressed up like a Disney character, they could potentially be mistaken for a cast member by other guests. This is obviously a problem for a company that has created and cultivated hundreds of characters.
While full face masks will still only be allowed for guests younger than 14, anyone can dress up from head to toe in a full costume during the upcoming fall season during their Not So Scary Halloween Party.
While Disney has relaxed the costumer rule this fall, please remember that “All Guests may dress as their favorite character, but may not pose for pictures or sign autographs for other Guests.”
Additional information on mask policies and dress code can be found here.