Mark wondered just who got turned into an old man that left such an impression with Korra, because he remembers all the body swapping before the aging and de-aging... though he remembers the power swapping first.

"No, uh, I think for a while I was the Avatar.... Or at least, I had your powers." He paused. "...I almost lit my house on fire."

Thankfully, he lived in the Earth sector and that was very, very hard to do.