So, personally, i think this speaks to his larger outlook on relationships and general emotional compacity and would most definitely think this was concerning. I feel like a lot of the responses here are latching onto your ages and saying "you're too young to move in together anyway," but I don't think that's what they should be focusing on here. He doesn't think couples shiuld move in together at all until marriage, believes couples that do are "troubled," and he believes beong forced to live with his significant other would cause him to become unnatracted to her. It speaks to a greater misunderstanding of relationship dynamics and hints that he has a pretty negative veiw on partnership. I would be concerned that he thinks he would lose attraction to some if he were to live with them. Why? Because you're forced to see that they're a human doing everyday human things and not some pretty mannequin? So if you're married that magically lifts the threat of losing your attraction for your significant other if you live together?

I would for sure open some dialogue about this, there's a possibility that there's some unfortunate information looming under his words, or he could just be terrible at expressing himself. I wouldn't just write this off though.