It seems to me that in constructing an answer to that question, we are weighing our social and developmental progress against the ages we generally associate to

It seems to me that in constructing an answer to that question, we are weighing our social and developmental progress against the ages we generally associate to social and developmental milestones. It's a bit like asking someone how far they have walked today. They aren't going to go back and count the steps. Instead, they will consider what landmarks they passed, and what events they encountered, try to add them all together, and compare that sum against other distances traveled that they do have explicit measurements for. The length of a journey is most often described, not as an accounting of unit measure, but from weighing the complexity of the story one would tell about it. This kind of narrative measurement is already present in most of our conversations about age. What age do people learn to read, to swim, or to ride a bicycle? How old is a grandparent? Are you too late in life to start a family? When should a person begin retirement? All of those narratives set a rubric of expectations: a domain and scale for age itself. When we ask someone how old they "feel", we are intentionally vague. We are asking for the "age" that isn't defined by time. So a person constructs a new definition or of the narratives that are familiar to them, and tells us where they see themselves in that collection of narratives.