a complete lack of context and zero understanding of human norms. Literally has to be told that murder (along with other actions) is bad. If those aren't childlike traits I'll eat my hat. Sure he can walk and talk and feel, but that's so he is a functioning character. He looks at sex and has zero comprehension(he can see the actions, but understands nothing). Gaider wrote the character with a certain image in mind and I think he achieved that. And after he articulated that, how can you be shocked that he's a little disgusted?
I never thought of Cole as a child, more like an adult (teen?) with mental problems.
He had amnesia, that's the first thing you learn about him. He can't remember who he is or how he ended in the tower. But an adult with amnesia is not a child. Not knowing or understanding laws or morals doesn't make you a child either. If you pick any adult and send him to a foreign country, he will most certainly not understand some of their customs. Hell, look at Morrigan in Origins, she finds ridiculous half the things you take for granted (maternal love, good manners, sympathy...). Is she any less of an adult for that?
I don't think he doesn't undestand sex either. He may not be interested in it, but that's a different matter. I can't remember, but, doesn't he feel embarrassed when Evangeline finds out he saw her nude? Which means that, even if it wasn't a sexual act for him, he knows it could be considered sexual.