The body has its journey. So does the mind.
The journey you know
Teeth come in. Limbs lengthen, bones set, a voice drops. Later, things wear down. It happens in roughly the same order for everyone, and nobody has to be taught it.
The journey you don't
The mind has a growth of its own: not what it knows, but the shape of how it makes sense of things. That shape changes across a lifetime, and after childhood it has very little to do with age.
This is a map of that second journey. Not a test, and not a ladder. Each stage is a whole way of making sense of the world, with its own powers and its own blind spots. We don't grow by leaving earlier stages behind so much as by becoming able, at last, to hold what used to hold us. Move through it at your own pace.
The pull toward connection: belonging, being part of something larger than ourselves.
The pull toward distinctness: self-containment, standing as one's own person.
Development swings between these two pulls, all life long.
The path below zig-zags for a reason.
Up to here, the stages arrive in a fairly reliable order, tied to age. From here on, they don't. The coils widen, and where we stand has little to do with how old we are.
After childhood, where we stand has little to do with age. Most of us live somewhere between the Socialized and Self-Authoring minds; the Self-Transforming mind is rare. Every move gains something and costs something. There is no finish line here, only a longer view.
Sources
Drawn from Robert Kegan's constructive-developmental theory: The Evolving Self; Kegan, Noam & Rogers, "The Psychologic of Emotion"; and Kegan's "Hidden Curriculum of Adult Life" lecture.