Why does the speaker of "sailing to byzantium" want to abandon his mortal body? (support position with evidence)

The speaker wants to abandon his mortal body because bodies as they age become old, raggedy, and useless. He says "An aged man is but a paltry thing, A tattered coat upon a stick". This shows how much he dislikes his old body and wishes to "But such a form as Grecian goldsmiths make", which means he thinks that in Byzantium he will take the form of a golden statue.