Numbers are important for both counting and measurement, and today we start discussing measurement in the familiar context of time and the phases of a human life. This is not a bad place for young people to start learning about a scale and different units to measure something.
We begin by explaining how the fundamental units of a day, month and year come about from the relative motions of the earth, moon and sun. Then we lay out a linear scale representing 100 years, the rough potential life span of a human (although some people do live beyond that). On this time scale we can point out various important times and stages of life.
This is a good way for students to engage with numbers and their relation to their own lives and others around them. It is also a place to mention some interesting facts related to life spans of very long-lived creatures (like the bowhead whate), and also to talk about average life expectancies, such as 18 years for a domestic cat.