Luke 3:23 (ESV)
23 Jesus, when he began his ministry, was about thirty years of age, being the son (as was supposed) of Joseph, the son of Heli,
Why did Jesus begin his ministry when he was about 30 years old? Why not earlier? Why not later? What was he waiting for and why?
Why did Jesus begin his ministry at age 30?
Jesus a sympathetic High Priest that can sympathize with our weaknesses. For this reason, he came to earth born as a man having flesh and blood, and experiencing life as a human, having feelings and emotions at first hand.
Hebrews 4:15 (NASB)
15 For we do not have a high priest who cannot sympathize with our weaknesses, but One who has been tempted in all things just as we are, yet without sin.
Why 30 years?
The census of the Kohathites taken at Mount Sinai indicated that the service for priesthood included those between the ages of 30-50.
Numbers 4:2-3 (NET Bible)
2 “Take a census[a] of the Kohathites from among the Levites, by their families and by their clans, 3 from thirty years old and upward to fifty years old, all who enter the company[b] to do the work in the tent of meeting.
The following are from the footnotes Numbers 4:3 NET Bible.
The second census of Levites now will focus on those between 30 and 50 years of age, those who were actually in service. These are the working Levites. The duties here will be more specific for each of the families. The Kohathites, although part of the ordinary ministry of Levites, were a special group chosen to handle the most holy furnishings. J. Milgrom shows three aspects of their service: (1) skilled labor (מְלָאכָה, melaʾkhah) or “work,” (2) physical labor (עֲבֹדָה, ʿavodah) or “service,” and (3) assisting the priests (שָׁרֵת, sharet) or “ministering”
The (currently accepted) answer by @OzzieOzzie is just plain wrong.
At this time, one had to be approximately 30 years of age to become a Rabbi. This recorded in the Code of Jewish Law (O.C. 581:1), which was being written at that time, along with the codification of the Talmud.
You can read more about this over at mi yodeya where the user GershonGold comments:
The Rashbam explains that at 30 one is worthy of leadership.... Orach Chaim 581:1 mentions that a Baal Tefila for the High Holy days should be at least 30. The Mishna Berura explains that at 30 one is humble and broken hearted.
Furthermore, in Jewish though, God had commanded people to "be fruitful and multiply" (you can read more about Talmudic ideas of this here and here), and although no one would want to forbid a man from becoming a Rabbi due to lack of being married and having children, it was strongly encouraged. Of course this required you to be of an age - mid to late twenties - whereby you at least had the opportunity to experience "first mitzvot of the Torah" (ie, "be fruitful and multiply"). (Reference: this is mentioned in Satlow's Jewish Marriage in Antiquity, but it's a big book and I'll have hunt it down later).
There are more reasons (such as having to have experienced a significant amount of life, etc). But ultimately one could not lead a Rabbinical school, nor lead services on one of the High Holy days unless they were 30.
Jesus - a Jewish Rabbi - would not have been accepted at all unless he was at that age.
Jesus' lineage shows him being of the tribe of Judah; He is in line for being king. He absolutely does NOT qualify as a priest, who are required to be sons of Aaron (ie, Levites).
The reference to Jesus as "High Priest" is clearly stated as something entirely separate from the Levitical regulations. Paul talks about this at length in Hebrews 5-7, and even the prophecies of the Messiah mention that Messiah would be a priest - but NOT of the sons of Aaron; Messiah would be "in the order of Melchizedek" (Psalm 110:4). In fact, Hebrews explicitly says Jesus was NOT of the Levitical order (Heb 7:11):
If perfection could have been attained through the Levitical priesthood—and indeed the law given to the people established that priesthood—why was there still need for another priest to come, one in the order of Melchizedek, not in the order of Aaron?
There are no such requirements for "being of the order of Melchizedek".
This distinction is crucial, because there are differences in the priesthoods. For example:
Jesus's life and ministry often included events that reflect various messianic patterns established in the Old Testament. It turns out that the age at which Jesus began his ministry may also follow that trend.
There are two messianic figures that both began their ministries at age 30.
David when he began to reign:
4 David was thirty years old when he began to reign, and he reigned forty years.
-2 Samuel 5:4
Joseph when he entered into the service of the Pharoah to save the world:
46 Joseph was thirty years old when he entered the service of Pharaoh king of Egypt. And Joseph went out from the presence of Pharaoh and went through all the land of Egypt... 57 Moreover, all the earth came to Egypt to Joseph to buy grain, because the famine was severe over all the earth.
-Genesis 41:46-57
NOTE: Very fascinating book Messiah Ben Joseph by David Mitchell that details the Jewish tradition of the Messianic Joseph and his descendant Joshua that is deeply rooted in the Old Testament scripture.
NOTE: Regarding other answers posted. I don't believe that the 30 year age requirement in Numbers 4 relates since none of those temple workers were priests and I also don't think Jesus's starting age has much to do with rabbinic tradition since Jesus was more considered with fulfilling the scriptures than the doctrines of men.
Well since my last answer wasn't understood it seems I'll have to spell it out. Jesus died at 30 Years because there exists prophecy in Scripture that Jesus would die after 5,500 Years from Adam.
This timeline is embedded within the creation week of Genesis 1:1-2:3 which represents an historical timeline of 7,000 Years. This is because God told Adam:
"but from the Tree of the Knowledge of Good and Evil you shall not eat, for in the day you eat if it you will surely die." Genesis 2:17 (emphasis added mine)
And when did Adam die?
"So all the days that Adam lived were 930 Years, and he died." Genesis 5:5
Seeing that Adam died in the day he ate of the forbidden fruit: each day of the week represents a period of 1,000 Years. So then God from the very beginning wrote that there would only be 7,000 Years of recorded history.
And we see that Adam was created in the middle of the 6th Day while the animals of the earth were created in the beginning of the same day (Genesis 1:26-28); and, while not explicitly stated we can draw this conclusion from the fact that instead of God creating everything instantly He spread out everything over a 6 Day period, and since this is so we may also safely say that it took God some time to form all of the animals; and, and since this is so it is not hard to believe that God gave Adam dominion over all the animals and the earth at the end of the 6th Day.
All this means that after 5,500 Years Christ would die and rise from the dead: this we see in the creation week for exactly 3 Days and 3 Nights prior man did not exist and God was creating the earth and the plant life from the ground (Genesis 1:9-13). And when Adam was created from the dust of the ground: this is a shadow of Jesus Christ's resurrection from the dead. Adam is a type of Christ for he and Eve are the only people to not have earthly parents give birth to them, therefore this makes Adam the Son of God and the first type of Christ who is the new Adam. And after 6,000 Years Christ would return to rule the earth for 1,000 Years.
We also see proof of this in the dimensions of the Ark of the Covenant, in cubits, which add up to 5.5 Cubits (Exodus 37:1) which are 5,500 Years before Christ would come in the flesh and die for our sins. The final proof of Christ dying 5500 AM is in Daniel's 70 Week prophecy where he gives us the exact year Christ would die:
"So you are to know and discern that from the issuing of a decree to restore and rebuild Jerusalem until Messiah the Prince there will be seven weeks and sixty-two weeks; it will be built again, with plaza and moat, even in times of distress. Then after the sixty-two weeks the Messiah will be cut off and have nothing, and the people of the prince who is to come will destroy the city and the sanctuary. And its end will come with a flood; even to the end there will be war; desolations are determined." Daniel 9:25-26
So this means that Daniel is beginning his count from the time of Cyrus the great as he foresees the delays in temple construction, being done in times of distress, and therefore says this will happen in a 7 Week/49 Year period; that is why he says after 62 Weeks/434 Years the Messiah will die (see interlinear Hebrew to confirm that Messiah, and not Prince, is used).
Now if we count all of the years from Adam to the death of Christ according to the longer chronology in the Septuagint/LXX then we get 5,500 Years; but according to the shorter chronology found in the Masoretic Text there are 4,034 Years for the same period. Here is a breakdown of the LXX reckoning:
Cyrus began his reign in the year 5017 AM and 483 Years later Christ would die 5500 AM. We may verify this to be true when we look at the reigns of Augustus and Tiberius. Augustus came into power in the 184th Olympiad while Christ died in the 202nd Olympiad, which is also the 15th Year of Tiberius. Therefore this is a span of 72 Years which means Jesus was 15 Years old at the death of Augustus and the 1st Year of Tiberius; and died at 30 Years old in the 15th Year of Tiberius. This then would mean that the Ptolemaic dynasty lasted for only 280 Years; Alexander the Great ruled for 12 Years from the 111th Olympiad to the 114th Olympiad; and from Cyrus to the end of the Persian kingdom is 119 Years. And 1 Olympiad = 4 Years.
So it is clear that God planned for Jesus to die at 30 Years old 5,500 Years from Adam. And when you check the time of His death against history it all adds up. And finally this prophecy was given cryptically to Adam and Eve when they were in the garden of Eden:
"And I will put enmity between you and the woman, and between your seed and her seed; He shall bruise you on the head, and you shall bruise Him on the heel.” Genesis 3:15
There is a simple answer: John the Baptist had to come first and fulfill the role of Elijah.
The disciples asked him, “Then why do the scribes say that first Eli′jah must come?” He replied, “Eli′jah does come, and he is to restore all things; but I tell you that Eli′jah has already come, and they did not know him, but did to him whatever they pleased... 13 Then the disciples understood that he was speaking to them of John the Baptist.
The reason that religious authorities insisted Elijah much come before the Messiah is the prophecy of Malachi 4:5-6
Behold, I will send you Eli′jah the prophet before the great and terrible day of the Lord comes. And he will turn the hearts of fathers to their children and the hearts of children to their fathers, lest I come and smite the land with a curse.
We don't know exactly how long John's ministry lasted before Jesus came to be baptized by him. But apparently he had done enough, even though he had not yet 'restored all things' for Jesus to feel that it was time to begin his own ministry on John's foundation as his forerunner.
