Albert Barnes Commentary Psalms 92:14

"They shall still bring forth fruit in old age; They shall be full of sap and green:" — Psalms 92:14 (ASV)

They shall still bring forth fruit in old age - Just as a tree that is carefully planted and cultivated may be expected to live long and to bear fruit even when it is old. It is true that such a tree may be cut down; or that it may be blown down by winds and storms; or that it may be unproductive. But, as a general rule, and as laying the foundation of a reasonable hope, such a tree may be expected to live long and to produce fruit even when it is old.

So it is with one devoted early to God and trained up under the influences of religion. The care, the culture, the habits of temperance, of industry, of moderation, and of sobriety so formed, are favorable to length of days and lay the foundation for usefulness when old age comes.

An aged man should be useful. He should feel that whatever wisdom he may possess from long study and experience belongs to God and to truth. He should recognize that one great reason God spares him is that he may be useful. The world needs the benefit of his counsel and his prayers. His life is extended not for his own ease or enjoyment, but so that virtue and piety may be extended in the world by all the influence he can bring to bear upon it in advanced years.

It may be added that, as a matter of fact, those who are trained in this way and are preserved in this way are useful in old age. No one spared in this manner needs to be useless; perhaps almost none are. There is something appropriate for old men to do, just as there is for the young and the middle-aged; and it should be the goal of an aged Christian to find out what that is and to do it. The word translated “old age” literally means “grey or white hair.”

They shall be fat - The meaning is that they shall be vigorous, or have the appearance of vigor and health.

And flourishing - The margin, as in Hebrew, notes “green.” This image is taken from a tree, as if it were still green in old age, or gave no indications of decay.