Do you feel there's a critical life-stage or period of development where personality becomes entrenched?
Is there a point (puberty, perhaps) where one's type is "defined" and reaches maturity?
Most "empirical" personality tests shy away from assessing kids. They claim it's unreliable, and I'd agree. Children show tendencies, but early on, brains are really plastic things. That said, thinking back to adolescence, I recall many friends and peers who fundamentally became very different people. I'm not talking subtype swaps or anything like that; I mean full-on type-shifts.
Obviously, hormones do a number on the brain during puberty; but just about everything is changing then. Is there something pivotal and defining about this (or any other) stage of development? Could a few crazy years toss out "the type we were" and determine "the type we become?"