Between the mid-teens and the mid-twenties, the human brain records an unusually rich collection of memories—not because it works better than before or after, but because life is packed with firsts that rarely happen again.

Between the mid-teens and the mid-twenties, the human brain records an unusually rich collection of memories—not because it works better than before or after, but because life is packed with firsts that rarely happen again.

Ask most adults over forty to list the memories that come back to them unprompted, and a strange pattern shows up. They do not distribute evenly across a life. They cluster. Disproportionately, they come from somewhere between the ages of about ten and thirty, with the heaviest concentration falling in the mid-teens to mid-twenties. Childhood before that stretch is thin. Middle age after it, despite being longer and often busier, produces compar…