Matthew 4:18-22
While walking by the Sea of Galilee, he saw two brothers, Simon (who is called Peter) and Andrew his brother, casting a net into the sea, for they were fishermen. And he said to them, “Follow me, and I will make you fishers of men.” Immediately they left their nets and followed him. And going on from there he saw two other brothers, James the son of Zebedee and John his brother, in the boat with their father, mending their nets, and he called them. Immediately they left the boat and their father and followed him.

In most translations of the Bible, this passage is headed “The calling of the first disciples”. If you think about that though, it’s probably not entirely true.
Jesus was already a known teacher, and had been traveling around and preaching the Kingdom of heaven for a bit. He began preaching when John the Baptist was arrested. Many of John’s disciples may have started to follow Jesus with their leader in jail.
Also, Christ probably had others that chose to follow him at that time, but he just isn’t recorded as specifically calling them. He did call the four men in the passage.

So this may be the calling of the first named disciples, but they may have not been the actual first disciples.