Dora Bas Rivka Silver O'H
In this Psalm, David directs all of G-d's various creations to praise Him: angels of various ranks, celestial spheres, the heavens, the waters and more are all called upon to sing to Him for saying the word and causing them to exist. G-d has set the universe in motion and His program will not change. Just as the things above should praise G-d, so should the things below: sea creatures, fire and water (in all its forms), mountains and trees, birds and beasts - oh, yeah, and people, too. David specifies the kings of the various nations and their officers, because in the Messianic era, everyone will recognize G-d.
Young men and young women, who are normally preoccupied with the things that preoccupy youth, will all praise G-d. Old men and young men will praise Him together. (It doesn't say that the young men and women will do so together for reasons of propriety, just as the Temple had, and our synagogues have, separate sections for men and women.)
G-d alone will be praised. (Not only does this preclude idols, but even the rulers of nations will forgo honor in favor of G-d.) G-d will have raised the prestige of Israel, who were formerly humbled in exile, and He will cause His adherents to be praised. Therefore, the Jewish people, who are close to G-d, should praise Him!