The first Osho book I have ever read, was Maturity. I started to read it in the store, and fell in love with it.
It echoed one of my favorite Landmark courses, the Wisdom Course.
In that course, maturity was a state (they call it possibility, just a Landmark word!): where you were using adult capacities to live your life.
One would think that when you are an adult you use your adult capacities, but that is not the case.