Snicklefritz

Within that period between adolescence and old age dwells different types of people all gathered together in one body, one brain, and one soul. No, that does not imply that we are all suffering from multiple personalities. The book is about the kinds of experiences that a person might have according to that person's age, geopolitical place in time, and interests, which also change with time.
Lewis Carroll alluded to the phenomenon; consider Chapter V, 'Advice from a Caterpillar' of "Alice's Adventures in Wonderland" wherein:
"Who are you?" said the Caterpillar.
Alice replied, rather shyly, "I - I hardly know, Sir, just at present - at least I know who I was when I got up this morning, but I think I must have been changed several times since then."'
Do you know what kind of person you were when you woke up this morning? Are you that same person now?