Some clarification is needed here again. While Paul did immediately begin proclaiming Jesus as the Christ based on his personal encounter with Jesus and while he continued to gain strength, he also did have an opportunity to be with Peter shortly afterwards before going away to Tarsus for years. So it’s safe to assume that Paul’s early message was fundamental in nature and not fully mature and that in his brief time with Peter and the other Apostles, they did teach him some things. However, the core of his message to the Gentiles was not yet present, and must have come later, because he would have had the opportunity to check it out with Peter and the others at that time rather than have to return 20 years later for a message validation as he did.
Here’s scriptural proof that Paul did meet with Peter early on.
From Acts:
"Now (
AD) for several days he was with (
AE) the disciples who were at Damascus, 20and immediately he began to proclaim Jesus (
AF)in the synagogues, saying, “He is (
AG)the Son of God.” 21All those hearing him continued to be amazed, and were saying, “Is this not he who in Jerusalem (
AH)destroyed those who (
AI)called on this name, and who had come here for the purpose of bringing them bound before the chief priests?” 22But Saul kept increasing in strength and confounding the Jews who lived at Damascus by proving that this Jesus is the Christ. 23When (
AJ)many days had elapsed, (
AK)the Jews plotted together to do away with him, 24but (
AL)their plot became known to Saul (
AM)They were also watching the gates day and night so that they might put him to death; 25but his disciples took him by night and let him down through an opening in the wall, lowering him in a large basket. 6(
AN)When he came to Jerusalem, he was trying to associate with the disciples; but they were all afraid of him, not believing that he was a disciple. 27
But (AO)Barnabas took hold of him and brought him to the apostles and described to them how he had (
AP)seen the Lord on the road, and that He had talked to him, and how (
AQ)at Damascus he had (
AR)spoken out boldly in the name of Jesus. "