Why did Jesus wait thirty years to begin his public life?
Jesus wanted to share a normal life with us and thus sanctify our everyday routine.
Jesus was a child who received love and affection from his parents and was brought up by them. Thus he increased "in wisdom and in stature, and in favor with God and man" (Lk 2:52); he belonged to a Jewish village community and took part in its religious rituals; he learned a trade and had to prove his ability as a craftsman. The fact that God in Jesus willed to be born into a human family and to grow up in it has made the family a place where God is present and a prototype of a helping community.
(From Catholic Youth Catechism question 86)