30

In tennis, the number 30 represents the second point gained in a game

30 is the minimum age for United States senators

The number of uprights that formed the Sarsen Circle at Stonehenge

30 is the total number of major and minor keys in Western music

The number of tracks on The Beatles' White Album

30 is the country code for Greece

Calvin Coolidge was the 30th US President.

30 years of marriage is the pearl anniversary

A polygon with thirty sides is called a triacontagon

30 tends to be the maximum age for seals

There are 30 days in the months April, June, September and November 

30 is a Harshad number it is divisible by the sum of its digits 

The atomic number of zinc is 30

30, when surrounded by hyphens indicates the end of a newspaper 

The star Gamma Pavonis is 30 light years away

30 is the atomic weight of the element phosphorus

In binary, 30 can be written as 11110

30 is the number of variations in Bach's Goldberg Variations

Cats have 30 teeth

30 is the number of known natural satellites of the planet Saturn

In Roman numerals 30 is XXX

30 is the total number of answers/questions in each of the first stages of Jeopardy

In Back To The Future Marty McFly travels back 30 years

30 degrees C is 86 F

Wisconsin was the 30th state

30 is a semi-perfect number

In the game of Bingo, the ball 30 is known as “Dirty Gertie, Blind 30”

30 is a stage in young adulthood

Jack Weinberg coined the phrase "don't trust anyone over 30"

and...

Today...I am 30.