Luke 3:23

Luke probably mentioned the round number "30" to describe Jesus’ age when He launched His ministry because many significant Old Testament characters began their service of God when they were 30 (cf. Genesis 41:46; 2 Samuel 5:4; Ezekiel 1:1). This included Israel’s priests (Numbers 4). Evidently Jesus was 32 years old when He began His ministry. [Note: Hoehner, pp. 37-38.] Luke also clarified that Jesus was not the physical son of Joseph. People only supposed that He was.