Board Thread:Questions and Answers/@comment-26848457-20150802191529/@comment-10733658-20161216215308

I'm sorry, but all information on half-humans we have so far shoots that idea down. They cannot regenerate, or survive extreme damage like a ghoul can. Their lack of regeneration is one of the things that separates them from OEGs. Arima and Hairu were tough, but still died like ordinary humans would. Uta, on the other hand, possesses ADVANCED healing abilities.

There's also the fact that he's too old. We don't know his exact age, but we have enough information to place a ballpark. He was stated to be in his late teens during the flashback chapters, only a few years younger than Arima. If he were a half-human, he'd be close to dying from old age.