According to the Gospel of Luke, Jesus was about 30 years old when he began his public ministry.
Luke 3:23 gives this age while introducing Jesus after his baptism and genealogy. The wording is approximate rather than a precise birthday record: Jesus was “about thirty years of age” when he began his work. Luke then presents a ministry that includes teaching, healing, travel through Galilee and Judea, and the journey toward Jerusalem.
The age is significant because thirty was an established age of maturity in several biblical and Jewish contexts. The Hebrew Bible also describes Levites beginning certain service at thirty in some passages, although Luke does not explicitly say that Jesus’ age is modeled on that practice.
The other Gospels do not state Jesus’ age when his ministry began. Luke’s figure should therefore not be confused with a calculated exact age based on a complete chronology. It is the Gospel’s approximate figure, not a modern biographical date.