“Jesus was about thirty years old when he began his public ministry” (Luke 3:23 NLT).

THE SIGNIFICANCE OF THIRTY YEARS
With the exception of the birth accounts in Matthew and Luke and the twelve-year old in the Temple account in Luke, the gospels contain little detail about Jesus before thirty. All four gospels focus their attention on Christ’s ministry that began with His baptism at thirty and concluded with the cross, the tomb and the ascension three years later. So, why was it significant for Jesus to begin His public ministry at age thirty?
 
Perhaps these examples from Scripture will shed light on this question:
1) Joseph was thirty when he began serving as Pharoah’s second-in-command over Egypt (Gen. 41:46).
2) Levite priests began their public ministry at age thirty (Ex. 4:3).
3) David became king at age thirty (2 Sam. 5:4).
4) Ezekiel the prophet saw his first vision at thirty (Ez. 1:1).
 
While the Bible doesn’t answer our question directly, perhaps we might infer by example and type that thirty is the biblical age for one to be publicly acknowledged as a prophet, priest or king. For in Jesus, we see all three offices fulfilled.
 
It was on my thirtieth birthday that I first studied these Scriptures and finally answered the call of God that had been on my life since I was a boy.