Each child is different - work from the little things & go up to the bigger things to see if they can handle them. DS was certainly tall enough at 5, but there was no way that he was ready for ToT at that time.

DS (12) is standing right next to me & said, "NO WAY at 5"! But that's just him . . . I should add that now it's among his favorites at Disney! As another note, I was 41 before I got the guts to try this one - and now it's my favorite! This is the only attraction at Disney that can make me "scream like a girl".