Nine in the second place means

A dry poplar sprouts at the root.

An older man takes a young wife.

Everything furthers.

Wood is near water; hence the image of an old poplar sprouting at the root. This means an extraordinary situation arises when an older man marries a young girl who suits him. Despite the unusualness of the situation, all goes well.

From the point of view of politics, the meaning is that in exceptional times one does well to join with the lowly, for this affords a possibility of renewal.