Kids are all just so different. Mine (almost 4) seems fearless at home, but is absolutely terrified of Barnstormer because it's loud*. He hates the dark drop in Pirates and will not ride it (we go frequently - live close - and we haven't ridden it in over a year!).
He likes 7 Dwarves okay, because it's smooth and quiet, but it's not a must-do.
He is definitely not ready for Big Thunder or Slinky, though he's tall enough for both.
*he also really struggles with MMRR because of the explosion in the preshow. We often skip it because he's in tears in the line. I have tried showing it on YouTube and he leaves the room at that part. Bless!