"I was a teenager, a long time ago. About seventy years ago, in fact." He frowns at Aang. "Yet you don't look a day older than when we ended the war... How can that be?"

More Spirit World interference? Even so, if Aang was here from the Spirit World, he shouldn't be this young or be missing so many memories... And what about Korra? Even if she did have access to her past lives again, there's no sign this is Aang's spirit he's talking to through her. It would make no sense.