Answer
Luke 3:23 informs readers that “Jesus himself was about thirty years old when He began his ministry.” Bible historians pinpoint Jesus Christ’s birth between 6—4 BC and the start of John the Baptist’s ministry around AD 28, making Jesus just over thirty years old when He began His public ministry.
As the Jewish Messiah, Jesus was a descendant of King David from the tribe of Judah (Matthew 1:1–17; 2:1–6). According to ancient Jewish law and custom, thirty years was considered the age of full maturity, physically and mentally, and suitable for high degrees of responsibility: “David was thirty years old when he became king” (2 Samuel 5:4); “Joseph was thirty years old when he entered the service of Pharaoh” (Genesis 41:46). The Jewish Levites began their priestly service at age thirty (Numbers 4:3, 23, 30, 35).
It would be reasonable to assume that Jesus began His public ministry at thirty years of age simply because this was God’s timing and purpose (and, certainly, it was). Everything Jesus did was in obedience to His Father’s will and plan (John 4:34; Hebrews 10:9). However, a practical explanation attributes our Lord’s delayed ministry start to His position as a Jewish rabbi. Thirty was also the age at which Jewish scribes and rabbis were regarded as mature enough to enter their office as teachers (van Oosterzee, J. J., The Gospel According to Luke: An Exegetical and Doctrinal Commentary, trans. by Lange, J. P., and Starbuck, C. C., Schaff, P., and Lange, J. P., ed., Wipf & Stock, 2007, p. 62).
Jesus had to be at least thirty years old if the experts in Judaism were to view Him as an authentic rabbi. Christ was called “Rabbi” by His own disciples (Matthew 26:25; Mark 9:5; John 1:49; 3:26; 4:31; 6:25; 20:16) and by John the Baptist’s followers (John 1:38). He was esteemed as a respected Jewish teacher. Even Nicodemus, a Pharisee and member of the Jewish high council, called Him “Rabbi” and recognized that Jesus was “a teacher who has come from God. For no one could perform the signs you are doing if God were not with him” (John 3:2). If our Lord had begun His ministry before attaining the acceptable and appointed age of priests, scribes, and other mature spiritual ministers, it’s likely that both the common folk and religious leaders of His day would have disregarded His authority.
Jesus waited thirty years to start His public teaching ministry because it was God’s time—the pivotal moment in all of history was primed to unfold (John 1:31–33; 2 Corinthians 6:2). Jesus had reached the culturally acceptable age of maturity and development. God would now reveal “the Lamb of God, who takes away the sin of the world!” (John 1:29), and no age-imposed barriers would be able to hinder the reception of Messiah’s teachings.
