Why do we teach Gentiles they were under the Old Covenant and the 10 commandments?

I realized 3 things today: a) I am a Gentile, b) the Old Covenant was made with the Jews and c) the 10 commandments was given as the Old Covenant and d) I was never ever under the 10 commandments or the Old Covenant. Yes I knew I was a Chinese. Told you 3 new things.