What is the theme of this poem below??

He wastes his time dreaming of the past and doesn't enjoy the life he has. He grows lean and drinks. While he is complaining of all the things he missed like knights, Medici, Priam, he is missing the great things that exist in his own time. A life thrown away dreaming about what he missed in the past. He should be sadder about the things he's missing in his own time.