Where the shape comes from
An old person whose hair has been left long and unbound, streaming out above the head, with a staff alongside. Long hair was the visible measure of years lived, so the one graph carries both readings: cháng, long in space and in time — 长城 the Great Wall, 很长 very long — and zhǎng, to grow up and to be senior — 长大 to grow up, 校长 a head teacher, 长子 an eldest son. Simplified writing cuts it to 长 in four strokes, keeping only the sweep of the hair and the stroke that crosses it.