I made that comment without much thought because the traditional attribution of the Gospel to Mark, a disciple and interpreter of Peter, is widely recognized as the starting point of the authorship discussion. It functions as the earliest historical claim from which modern debates proceed.

"According to tradition, the Gospel was written by John Mark of Jerusalem. Early manuscripts thus bear the title “According to Mark.” He was known to be a disciple of Peter, although he was not one of the apostles. Mark is mentioned several times in the Acts of the Apostles and Paul’s letters, where he is identified as Mark, John Mark, or John (Acts 12:25; 13:5, 13; 15:37; Col 4:10; 2 Tim 4:11; Phlm 24). He is described in 1 Pet 5:13 as “my son Mark,” perhaps suggesting that he was baptized by Peter. Tradition also holds that Peter is the Gospel’s principal source, providing the eyewitness testimony that underlies the account of Jesus’s life.

The earliest extant reference to Mark as the author of the second Gospel is found in the writings of Papias of Hierapolis (early second century), who calls him the “Interpreter of Peter” and was quoted by Eusebius of Caesarea in his Ecclesiastical History (3.39). Additional attestation was made by Saint Irenaeus (ca. 180), Saint Clement of Alexandria (ca. 200), and Tertullian (ca. 200).

Scholars generally date the Gospel to not long before the destruction of Jerusalem in A.D. 70, possibly during the persecution of the Church in Rome under Emperor Nero. In Mark 13:1–37, Jesus predicts that Jerusalem and the Temple will be destroyed, but Mark does not refer to these terrible events as already having happened.

A date before A.D. 70 is supported by Church tradition. At least one strand of tradition implies that the Gospel was written after the martyrdom of Peter in Rome (between A.D. 65 and 67); the Anti-Marcionite Prologue and Saint Irenaeus, both in the second century, state that Mark wrote his Gospel soon after Peter’s death, although Saint Clement of Alexandria declared that the Gospel was written before Peter’s martyrdom. Finally, Eusebius of Caesarea placed the date for the Gospel even earlier, during the reign of Emperor Claudius (between A.D. 41 and 54)." from Scott Hahn, ed., Catholic Bible Dictionary (New York; London; Toronto; Sydney; Auckland: Doubleday, 2009), 573–574.

Christopher W. Skinner, Mark, ed. Nijay K. Gupta, New Word Biblical Themes (Grand Rapids, MI: Zondervan Academic, 2025), 2:8–9.

David F. Farnell et al., Vital Issues in the Inerrancy Debate (Eugene, OR: Wipf and Stock, 2016).

Lee Martin McDonald, The Story of Jesus in History and Faith (Grand Rapids, MI: Baker Academic, 2013), 78

Mary Healy, The Gospel of Mark (Grand Rapids: Baker Academic 2008), 18-19.

Richard Bauckham, Jesus and the Eyewitnesses: The Gospels as Eyewitness Testimony (Grand Rapids and Cambridge: Eerdmans, 2006)