Kotario
The dilemma is completely unnecessary. The MCs behaving so dramatically that it appears if his deciding the fate of all human civilisation... Don't like. Simple. Like? Go for it. It's 'morally' correct as per the context after all.
Something to ponder: would a 80 year old intellect stay the same if forced to use a 13 year old brain? My assumption is that it would deteriorate. Also, a person's body affects often how we think, so I would imagine seeing her would be torturous since attraction is often based on hormones, which would be of a 13 year old.