Is this wrong?

So me and this guy started talk because of mutual friends and a mutual like of a sports team during a game. After the game we continued to talk every day and learn more about each other and the more I find out about him the more we find things in common and the more I like him. The only problem is I'm two months away from turning 20 and he turn 16 at the beginning of July. Most guys I've dated have been younger, but not this dramatic of a difference. He's a little bit older than my sister so I feel terrible for feeling this way about him, but I do and I need advice.