Boundaries of Curiosity
Curiosity can only reach out, extend itself toward self or other created boundaries of defensiveness, insecurity, doubt, protectiveness, 'absolutes' and fear.
Mental growth stops at the age a boundary forms. Overcome / remove the boundary and growth will continue.
This is how dogs were domesticated. Prevention of mental development results in a mature dog behaving as a puppy…
…Don't be a human puppy, as the saying goes.