A new worry

My daughter has a boyfriend. I'm calling it her first boyfriend. She says that she has had plenty of boyfriends in the past, but I'm not counting middle school "going out" as boyfriends. They never actually did anything together outside of school and hardly talked at school, so in my opinion, they were just crushes.

So here's what I know about this boy, we'll call him Sam. He is a Sophomore. 15 years old. Plays Lacrosse, good grades, honors classes, plays piano and guitar, parents are married and college educated. Sam seems nice, he was with the big group that I took to the haunted house last weekend and he was polite to the parents that were there and got along with all of A's friends. He came over on Sunday to play darts and had dinner at our house (A's BFF was here too). His mom dropped him off and made a point of coming in and meeting us before she left him with us. He came to A's choir concert on Monday night to watch her preform. He is helping to deliver our neighborhood newsletter tonight, having dinner with us and then he and A are going to the football game to meet friends there.

I am comfortable with this so far. They have never really been alone together and I am trying to treat him coming to the house just like I would treat any other friend coming to the house. My worry is that by letting him come over and hang out with the family I am validating this as a "relationship". A is only 14 and that is just too young for anything serious. I can't ignore that she has this boyfriend, and I can't really discourage it if I want her to keep sharing these things with us. But where is the line between accepting this and encouraging it?