Keats' brand of love is the stuff that romantic legends are made of… if only he could ever feel any of it himself. When Keats writes of love, it's not just of a pair of fine eyes. That would be waaaaay too easy. Nope, his love is HUGE and IMPOSSIBLE and always, always tinged with a healthy dose of despair. We get the feeling that Keats would have been a whole lot happier as a knight in shining armor, complete with a huge white horse. Turns out that the 19th century wasn't so full of castles and giants to conquer and damsels to rescue – so Keats is left dreaming of a love that ultimately remains available only in his imagination.
The speaker's vision of love is unrealistic. Even if he lived to a ripe old age, he would never experience the kind of love described here.