Yes you are doing the right thing, Its natural of a mother to look after their children especially if its a girl. Your daughter is too young to enter in a relationship with a guy much older than her. If your daughter insist that she really love the guy, I think just support her feelings I know time will come she will realize that their is more than that guy can give to her. If I were you, talk to the guy very often so that you will know him better because we can't tell at first impression will last, cause sometimes it wont.