Is it morally acceptable that he's actually an old man, or is it okay since he's a reincarnated?
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While seemingly similar to the "500 year old loli" problem, this "reincarnated thus horny" problem is slightly different, as while the loli problem questions the mental faculty and physical development of the questionable person, the reincarnate is not the questionable person (being mentally capable and physically developed beyond shota) - the target of his affection is the question. With that established, we will now move onto the target. Is she a loli? Nope. Then that ends the issue.
As a side note: author barely managed to redeem the story by the skin of their teeth. Unfortunately the redemption comes at a price of extreme escalation of conflict. All subsequent minor conflicts will thus become filler and be meaningless, annoying fluff detracting from the experience.