Here again is St. Peter speaking at the Council of Jerusalem. He could not be more explicit.
Acts 15:6-11: The apostles and the elders met together to consider this matter. After there had been much debate, Peter stood up and said to them, "My brothers, you know that in the early days God made a choice among you, that I should be the one through whom THE GENTILES would hear the message of the good news and become believers.
Call that a 'one-off', Peter wasn't the apostle to the Gentiles, Paul was:
15 But the Lord said unto him, Go thy way: for
he is a chosen vessel unto me, to bear my name before the Gentiles and kings, and the children of Israel: Acts 9
13 But I speak to you that are Gentiles. Inasmuch then as
I am an apostle of Gentiles, I glorify my ministry; Ro 11
15 But I write the more boldly unto you in some measure, as putting you again in remembrance, because of
the grace that was given me of God,
16 that I should be a minister of Christ Jesus unto the Gentiles, ministering the gospel of God, that the offering up of the Gentiles might be made acceptable, being sanctified by the Holy Spirit. Ro 15
15 But when it was the good pleasure of
God, who separated me, even from my mother`s womb, and called me through his grace,
16 to reveal his Son in me,
that I might preach him among the Gentiles; straightway I conferred not with flesh and blood: Gal 1
7 but contrariwise, when they saw that
I had been intrusted with the gospel of the uncircumcision, even as Peter with the gospel of the circumcision
8 (for he that wrought for Peter unto the apostleship of the circumcision wrought for me also unto the Gentiles);
9 and when they perceived the grace that was given unto me,
James and Cephas and John, they who were reputed to be pillars, gave to
me and Barnabas the right hands of fellowship, that
we should go unto the Gentiles, and they unto the circumcision; Gal 2
Though no doubt just as Paul would first visit the synagogue in every city he came to, Peter would also preach to Gentiles when/if the opportunity presented itself..