Can a 21-year-old guy date a 23-year-old lady despite their age differences?

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They’re in the same class, according to my sister, and she approached him on the first day of school to ask a question. But she recognized that, while he seemed calm, he had this attitude toward women. He maintains a respectful distance from them. He seldom talks to the girls in class unless they approach him, and he offers them direct, evasive responses. He’s really attractive (I’ve seen him a few times because my sister and I go to the same school), clever, and intelligent.

So when my sister informed me, I encouraged her to keep a distance from him, not ignore him, since we, too, grew up not like boys (no father and violent stepfather), but due to God and therapy, we’ve overcome it, and she has. She acted as though he understood it but didn’t know how to approach him because it’s usually the ladies that approach him first. Until something happened in their class (when I was there chatting with her) and she stuck up for someone. And the manner she went about it was so enticing that I was taken aback.

Because my sister is an extremely quiet person who seldom speaks and prefers to avoid crowds. I was surprised since, although being the youngest, I am the loudest. Her classmates began to notice her since she seldom speaks and prefers to remain in her corner observing. The guy wasn’t in class at the time, but she told me she met him at the door and tapped him, and he just smiled and said he heard what happened and was happy for her, my sister was startled and asked him how he knew, and he simply replied he has eyes around. And he’s the sort of man who wouldn’t want people or his male friends to see him talking to females or a lady, so when he said he has eyes around, it was odd, indicating that even if he and my sister seldom interact, his friends are aware of her.

So they become closer than they were at first, and most of the girls in the class are surprised at how cool he is around my sister. And now he makes it clear that he is extremely close to my sister, even if he relates to the other girls in the class, but not as deeply as he does with my sister, and he has even begun talking to me. They’ve grown closer, and you’ll often hear them debating (not to the point of fighting, but in a hilarious way) over little matters, both on the phone and in person. They don’t even notice when I’m around. And she claims that he has grown more open, that she has discovered the basis for his tough-man-against-ladies mentality, and that he can now laugh readily about little matters.

But now they’re cool, and I don’t mind that he’s my age mate, but I’d like to know whether they can be together. I’ve chatted with him numerous times, and while he’s young in age, he appears and acts older than his age. He sounds more like an older person than a 21-year-old boy, so I even call him a professor; he’s knowledgeable and picks his words carefully, and he’s always talking about my sister, and despite their age disparities, he says he likes her.

He’s really attractive and enjoyable to be around; he’s a fantastic fit for my sister because of how she is. I’m not sure how to tell her because she’s the sort that believes that “little things count,” even in friendship. So, please tell me whether it’s feasible for them to be so that I know how to proceed. So, does age actually make a difference in relationships?