Relationship gap or whatever?

So, I wanna hear people's opinion on this matter.

My friend who's a 23F likes a guy who is 17. Both of them have a thing for each other and there's a spark. But, I feel very awkward about such thing cause the guy is a minor and I feel he doesn't know what's right or wrong for his age.

My friend think it's normal though but, I was shocked and said it to her face that it's not normal and maybe it's called being groomed. I'm not even talking to her properly, probably because I feel disgusted. Is it just me or is it normal?