The sentence describes an old man sharing his wisdom with a younger generation. In this context, we need an adjective that describes high-quality, deep, or meaningful wisdom.
Sagacious (Correct): This means having or showing keen mental discernment and good judgment; wise. It is the perfect fit for someone sharing life lessons or profound knowledge.
Trivial: This means of little value or importance. It would be contradictory to "wisdom."
Ephemeral: This means lasting for a very short time. Wisdom is generally considered lasting and enduring, not fleeting.
Frivolous: This means not having any serious purpose or value; carefree and superficial.
Completed Sentence: "The old man shared his sagacious wisdom with the young generation."