“And Jesus himself began to be about thirty years of age, being (as was supposed) the son of Joseph, which was the son of Heli,”
Luke 3:23 — Greek Interlinear
Church Fathers on Luke 3:23
Having related our Lord’s baptism, he next enters upon the generation of the Lord, not bringing it down from the higher to the lower, but beginning with Christ, he carries it up to God Himself. Hence he says, And Jesus Himself began. For when He was baptized, and had Himself undergone the mystery of the second birth, then He is said to have begun, that you also mightiest destroy this first birth and be born in the second.
seeing He was pure, baptized by John, and at a time when His miracles had begun, that we might thence derive the lesson of purifying ourselves beforehand, and of embracing humility, and of not beginning to preach until the maturity of our spiritual and natural life. The first of these was said for their sakes who are receiving baptism; for although the gift of baptism brings remission, yet we must fear lest we return again to our vomit. The second is pointed at those who…
Or, He waited accomplishing the whole law until that age which takes in every sin, that none might say that He abrogated the law because He was not able to fulfill it.