True, except for one ride: Tomorrowland Speedway.
They have one height that allows kids to ride if there is a responsible older child or adult with them of a certain height. There is another height that allows kids to drive themselves.
The height requirements are there not because it's an estimation of the maturity of someone to handle certain rides. They're there strictly for the physical safety of the riders, due to the way the seats or the rides are constructed.
One example of a height requirement that is there only for physical and not mental reasons: the Dinosaur ride in AK. I think the requirement on that is a mere 36" or 38". Most kiddie rides are at the same height requirement. My DD, now almost 8 but then only 3, was about 40" tall, which was definitely physically "safe" for the seat structure on Dinosaur. However, I did not know, and DD certainly did not know, that Dinosaur may well be the scariest single ride (mentally) in all of WDW. It's extremely loud and intimidating, with lots of unexpected twists in the path. DD cried so hard afterward we had to buy one of the toy dinosaurs in the gift shop to placate her.
To this day she will not ride Dinosaur. I can't blame her.