A Jewish boy automatically becomes a bar mitzvah "son of the commandment" upon reaching the age of 13 years, and a girl upon reaching the age of 12 years. Technically, the term refers to the child who is coming of age, and it is strictly correct to refer to someone as "becoming a bar (or bat) mitzvah." However, the term is more commonly used to refer to the coming of age ceremony itself, and you are more likely to hear that someone is "having a bar mitzvah." In its earliest and most basic form, a bar mitzvah is the celebrant's first aliyah. During Shabbat  services on a Saturday shortly after the child's 13th birthday, the celebrant is called up to the Torah to recite a blessing over the weekly reading. The celebrant is also generally required to make a speech, which traditionally begins with the phrase "today I am a man." The father traditionally recites a blessing thanking G-d for removing the burden of being responsible for the son's sins (because now the child is old enough to be held responsible for himself).

And while we're on the subject, it is worth noting that the number 13 is not a bad number in Jewish tradition or numerology. Normally written as Yod-Gimel, 13 is the numerical value of the word ahava (love, Alef-Hei-Beit-Hei) and of echad (one, as in the daily prayer declaration, G-d is One!, Alef-Cheit-Dalet). Thirteen is the age of responsibility, when a boy becomes bar mitzvah. We call upon G-d's mercy by reciting his Thirteen Attributes of Mercy, found in Exodus 34:6-7. Rambam summed up Jewish beliefs in Thirteen Principles.

1.   G-d exists
  2. G-d is one and unique
  3. G-d is incorporeal
  4. G-d is eternal
  5. Prayer is to be directed to G-d alone and to no other
  6. The words of the prophets are true
  7. Moses' prophecies are true, and Moses was the greatest of the prophets
  8. The Written Torah (first 5 books of the Bible) and Oral Torah (teachings now contained in the Talmud and other writings) were given to Moses
  9. There will be no other Torah
 10. G-d knows the thoughts and deeds of men
 11. G-d will reward the good and punish the wicked
 12. The Messiah will come
 13. The dead will be resurrected
These are the 13 principles of Rambam.

When the Jim Carrey movie "The Number 23" came out, I was wondering why they did not focus on the number 13.

I edited my original post because I saw that my math did not add up. But drrnwynbchnbrgr posted some interesting numbers that have brought me to post back in what I removed. The year 2012 is said to be a humbling time for us all. I originally posted what I saw as a connection between 2012 and 13. I stated that the Maya's (and other civilizations) predicted that on Dec. 21 of the year 2012, bad things would happen. 12/21/12. I don' really know how I came up with the numbers, but I somehow added up each separation and came up with 13/13/13/. There is a post under general discussion 'All About 2012' that seems to support my thoughts.