For example, the "we" in "we were held captive under the law" (Gal. 3:23) appears to include Gentiles since in the preceding verse the state of being "under sin" is inclusive of both Jew and Gentile in Pauline writings (see especially Rom. 3:9). Here's the passage:
"22 But the Scripture imprisoned everyone under sin [hupo hamartian], so that the promise by faith in Jesus Christ might be given to those who believe. 23 Now before faith came, we were held captive under the law [hupo nomon], imprisoned until the coming faith would be revealed."
But how can Gentiles who are without law ("anomos", Rom. 2:12) be under the law? The answer is that if sin is a transgression of the law then being "under sin" means that one is subject to a penalty for transgressing an applicable law.
We have to remember that things like Shabbat are written into creation and are universal to all mankind (see Isaiah 66:23). There is one standard for man because, ab initio, G-d intended mankind to become one--even as He is One.