There is a geat amount of confusion among early Christian trdaition as to when Jesus died, some have said about 130 different opinions were held. The NT doesn't help pin it down as the dating in Luke doesn't work. Anyway the tradition that eventually won out was that jesus was baptised about 29/30 and killed 1-3 years later.
On another site someone speculated that it was Jewish tradition that indirectly helped establish this timeline. There seems to have been some significance to the year 30CE and the age of a hated prophet Balaam. The Sanhedrin was relocated to the marketplace because the temple had been damaged in an earthquake in 29/30 according to Yoma 39.
Shabb. 15a reads: "One hundred and eighty years before the destruction of the Temple
the wicked state spread over Israel. Eighty years before the
destruction of the Temple uncleanness was imposed in respect of the
country of heathens and glassware. Forty years before the
destruction of the Temple the Sanhedrin went into exile and took its seat in the trade Halls."
The Talmud (b Sanh 106b) gives the following indication concerning the age of a heretic at his death.
A certain heretic said to R. Hanina:
Have you ever heard how old Balaam was?
He replied:
There is nothing written about it. But from what is written
Men of blood and deceit shall not live out half their days [Ps. 55:23]
He must have been thirty-three or thirty-four years old.
He said,
You have answered me well. I have seen the chronicle of Balaam, and therein is written:
Balaam, the lame, was thirty-three years old when Pinhas the Robber killed him.
- Babylon Talmud, Sanh. 106b, quoted in Travers R. Herford,
_Christianity in Talmud and Midrash_ 1903, I, a; pg 72, item 15.
Tractate Yoma
Chapter IV
During the last forty years before the destruction of the Temple the lot [`For the Lord'] did not come up in
the right hand; nor did the crimson-coloured strap
become white; nor did the westernmost light [of the
Menorah] shine; and the doors of the Hekal [Sanctuary]
would open by themselves, until R. Johanan b. Zakkai
rebuked them, saying: Hekal, Hekal, why wilt thou be
the alarmer thyself? [meaning: predict thy own
destruction] I know about thee that thou wilt be
destroyed, for Zechariah ben Ido has already
prophesied concerning thee: Open thy doors, O Lebanon,
that the fire may devour thy cedars."
Is it possible then that the events of 29/30, coupled with the recurrence of the number "40" in Jewish mythology, helped fix the date for the Jesus baptism and death?