Sheloshim - mi yodeya?

Question

Who knows thirty?

Please cite/link your sources, if possible. After about one business day, I will:

• Upvote all interesting answers.

• Accept the best answer.

• Go on to the next number.

Answer 1

At 30 years one attains full strength (Avot 5:25)

Answer 2

Days before a Chag, particularly Pesach, at which one should begin studying the attendant laws.

Answer 3

30 are the years of the Levite draft (Num. 4:3).

Answer 4

• 30 letters (three times למשפחותיכם) is the width of each line in a Torah scroll. (Shulchan Aruch, Yoreh De'ah 272:2)

• 30 lines are used to write the Song of the Sea (Ex. 15:1-19) in a Torah scroll. (ibid. 275:4)

Answer 5

30 traits with which Malchut is attained (Avot 6:6)

Answer 6

"30 days in a year is considered a year"

http://www.mechon-mamre.org/b/l/l4501.htm on daf gimmel, amud beis

http://www.halakhah.com/pdf/nezikin/Makkoth.pdf on page 7

Answer 7

A person who vows to be a Nazir without specifying for how long, has to remain a Nazir for 30 days. (Nazir 5a)

Answer 8

30 days in a "full" month (notice a 29 day month is called "lacking" and a 30 day month is called "complete" -I'm sure there's some significance to that)

Answer 9

Gematria of the name "יהודה" is 30

Answer 10

As we see in מדרש תנחומא חיי שרה סימן ו, thirty out of the seventy nations were scattered during the דור הפלגה. To make up for this, thirty nations came from Avrohom: the twelve sons of Yishmo'eil, the six sons of Keturoh, the two sons of Yokshon (the second son of Keturoh), the three sons of Dedon (the second son of Yokshon), the five sons of Midyon (the fourth son of Keturoh), and the two sons of Yitzchok (Yisro'eil and Edom, obviously!), which also explains a different question.