What is meant by the line 'What to him are Plato and the swing of pleaiades?

This line, from the poem "Sailing to Byzantium" by W.B. Yeats, suggests that the narrator, an older person, finds more value in spiritual and enduring matters rather than in earthly pleasures or academic knowledge represented by Plato and the constellation Pleiades. It highlights a longing for something beyond transient human experiences.