No magical reason that memories could not be retained. There could be different ways to stay young or turn back time.
I think their conversation works either as brother or estranged, irresponsible resentful father.
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“If I had a world of my own, everything would be nonsense. Nothing would be what it is, because everything would be what it isn't. And contrary wise, what is, it wouldn't be. And what it wouldn't be, it would. You see?” -- Lewis Carroll, Alice's Adventures in Wonderland & Through the Looking-Glass