Classical Chinese medicine counts. Ages arrive in sevens and eights, cycles in sixties, vessels in threes and twelves — and the counting is usually load-bearing rather than decorative.
Read Suwen 1 with a pencil and write out the seven-year cycle as a table: age, state of kidney qi, what changes. The argument of the chapter becomes obvious once it is in columns.
Then do the same for the eight-year cycle given for men, which the chapter states without pausing to explain.