We cross lines without realizing they're being crossed, their divisions nothing tangible or neat. At the atomic level, even the crispest line is fuzzy. At the subatomic level, the line does not even exist until you name it.
When do we open eyes and see ourselves as different people? I remember finding myself no longer a child, now with face-lines and cocked-hip swagger and hip flask. The face is the same but the baby fat melts away showing more of the skeleton, more of the mind falling through the eye-lid droop. Name and region changes do not change the abnormalities of the malformed ribcage or the quirky bend in the nose. For those you need to break bones.