How 'bout this for a rule: if you're too young for Space Mountain, you shouldn't shoot a gun, period.
There's no age requirement for Space Mountain, just a height one.
Well, I was about
to write "if you're too short
to ride Space Mountain," but then realized I didn't want to be accused of anti-little people-ism.
So, okay, "unless you're a little person already over the age of ten, if you're too short for Space Mountain..."