Ecclesiastes 3:1 — "To every thing there is a season, and a time to every purpose under the heaven" — holds the full arc of life in a framework where every season has purpose, not just the seasons of active productivity. The season of active parenting is a season. What follows it is also a season with its own purposes. The problem with empty nest is not that the season changed — it is that the identity that was organized around one season has not yet discovered what the new season asks of it.
Psalm 92:14 — "They shall still bring forth fruit in old age; they shall be fat and flourishing" — is a portrait of sustained productivity that is not age-limited. The Hebrew dashen — fat, full of sap — describes a tree in mid-life vigor. The season after active parenting is not a season of diminishment in Scripture's framework. It is a season in which a different kind of fruit is possible — the fruit of accumulated wisdom, deeper prayer, service not organized around small children.
Commentary is from a charismatic Protestant perspective, drawing on KJV text and public-domain sources including Spurgeon, Andrew Murray, and Matthew Henry.