Are mature erythrocytes prokaryotic?
No.  Nobody considers red blood cells to be prokaryotic, perhaps most importantly because they are part of a eukaryotic organism.  Red blood cells begin life with the full complement of organelles, including a nucleus and mitochondria, but our RBCs shed their organelles during maturation.  In actuality, though, only mammalian RBCs lack nuclei; other animals' RBCs still hold on to their traditional eukaryotic characteristics.

As an analogy, apoptotic or necrotic cells don't have intact organelles, but they are still considered eukaryotic.