Paul certainly seems a very real character, who seems to have had a very real although hardly cordial connection with a guy named Peter. Nevertheless, Paul was under the very real impression that Peter had spent a good deal of time with this guy named Jesus. No proof of course, either way.
Some book I read a while back--can't exactly remember the title now--puts forth the observation that Paul never speaks of Jesus' life on earth, but only in a spiritual sense, "Jesus in us" type of phraseology, as one would speak of the Holy Ghost. The author thought that very significant.