My days; my hopes, and comforts, and happiness; days being oft put for happy days, or a happy state, as Psalms 37:18 Lamentations 5:21, as elsewhere they are put more generally for the events which happen in those days; in both which cases it is a metonymy of the adjunct. That declineth; or, that is extended or stretched out to its utmost length, as it is when the sun is setting, when it speedily and totally vanisheth. And just so the hopes of our restitution, which sometimes we have, are quickly cut off and disappointed.
Related Commentaries of Psalms 102:11
Psalms 102:11
11 My days are like a shadow that declineth; and I am withered like grass.