Numbers - Chapter 4

In Chapter 4 there is a census of the Levites.  In this census the men counted are those from thirty to fifty years of age - as this was the period during which they served.

Although Jesus was not from the tribe of Levi, he did have the role as our priest (he was a prophet, priest and king).

In Luke chapter 3 we read the genealogy of Jesus, and this begins:

"Now Jesus Himself began His ministry at about thirty years of age".