... and they stayed Jews all their lives. Paul says very clearly in Acts 28 that he IS a Jew, and faithfully kept all the traditions of Judaism all his life.
Did you miss 1 Corinthians? Chapter 9, verse 20 To the Jews I became as a Jew, in order to win Jews. To those under the law I became as one under the law (though not being myself under the law) that I might win those under the law. 21 To those outside the law I became as one outside the law (not being outside the law of God but under the law of Christ) that I might win those outside the law.
Paul clearly says he is not under the law. He also clearly says that he didn't keep the law at all times. He was free to keep it or not as part of his Christian freedom.