St. Peter was the first to baptize a Gentile, not St. Paul. And bear in mind this also:
"And when there had been much disputing, Peter, rising up, said to them: Men, brethren, you know, that in former days God MADE CHOICE among us, that by my mouth the Gentiles should hear the word of the gospel, and believe.
Seems that God did make choice among them and He chose St. Peter originally.
But Peter couldn't get it right all the time...And we all know that after that, Paul was assigned to the Gentiles while Peter was given the Jews for his ministry...