In The Great Gatsby, Jordan says,"Life starts all over again when it gets crisp in the fall." How is Jordan's statement ironic?

In traditional literary analysis, the season have specific symbolic interpretations: spring usually symbolizes rebirth, a new beginning, youth, innocence.  Fall is spring's opposite--fall brings the harvest, the end of summer, the "beginning of the end", nature starts to decline and die.  Fall is often associated with middle to late life.  It is ironic that Jordan indicated that life begins in the fall because it is counter-intuitive to the natural cycles of the earth and nature.