So here's a question for you all: starting from the assumption that a person's life can be broken down into distinct phases, 1) What are they and 2) What are the demarcations between them?

It's sortof a vague question, and it's meant to be. I mean, there's the classic sphinx approach (4 legs, 2 legs, 3 legs); there's the common parlance approach (infant, toddler, child, teen, young adult, middle-aged, old-aged); there's the simple approach (young, old); there's the family-based approach (living with your parents, living by yourself, living with your kids). There's a kindof depressing description I found once in a post-apocalyptic story - love (your parents caring for you), necessity (caring for yourself), duty (your kids caring for you). There's the 5 trees for the Sunrunners from the Dragon Prince series. There's... Well, probably more than I could write.

What "system" do you think demarcates a person's life best, from whatever point of view you choose?