Twelve years old - All males among the Hebrews were required to appear three times a year before God, to attend on the ordinances of religion in the temple, and it is probable that this was the age at which they first went up to Jerusalem, Exodus 23:14-17; Deuteronomy 16:16.
To Jerusalem - Where the feasts of the Jews were all held. This was a journey from Nazareth of about 70 miles.
After the custom of the feast - According to the usual manner of the feast.