I don't know about that. Judging what I've seen from DD's kindergarten and first grade classes, I think that depends on the kid. Like you, I still believe the characters are real, and I still get excited when I see them.
DD had boys in kindergarten telling her the Disney characters weren't real. In first grade this year, she had a girl telling her that only babies liked the Disney princesses and she shouldn't like them anymore. A boy told her he didn't know why she liked Disney so much because nothing was real and it was for babies. Luckily, my DD has a mind of her own and she told that girl that she could like what she wanted. As for the boy, she told him "Obviously, you've never been to Disneyworld" (he hasn't). Our niece decided she was too old for Disney princesses, and didn't like them anymore at age 6. Currently, all the first grade girls are immersed in Disney, but it isn't the classics or things you find at WDW. It is the live "tween" shows- I can not even tell you how many episodes I've seen of Good Luck Charlie, Austin and Allie, Jessie, and now Dog with a Blog.
I do think 5-8 is a fun Disney age though. I will say that from our yearly trips, aDD was easy and fun at age 2 and 3, a bit high maintenance at 4 and 5, and then back to being fun and easy at age 6. I'm hoping that DD is like you and I and never really grows out of the characters!