I'm laughing at this thread. We've never been to WDW, but have been to
Disneyland several times. The first time with the kids, my DS was probably about 8 or 9. He refused to go on HM -- was scared even before he got inside (I think from the music that plays outside). He stayed outside with my MIL, who didn't care to go either.
Our next trip, he was about 1 1/2 years older. I made him go, partly becuase no on else wanted to wait outside with him, and he cried all the way through it (mind you, he was about 9 1/2 or 10). His younger sister, who is almost 3 years younger, loved it even when she was 6. I haven't forced him to go again, and he always sits outside and waits for us to go.
He's now 22. I was talking to him about our upcoming WDW trip the end of September, which it without kids. He said, "Is there a HM there too?" I said yes, and he said, well, I guess it's just as good I'm not going then. He would still refuse to go. I don't get it, but something in his psychological makeup is very strongly opposed to this ride.