Because they needed a number between 12 and 14. If 13 should not have been invented, 3 (sacred number) neither.
No, I don't think your friends will hate you if you make out under 13 but at the same time why would you need to make out under the age if 13?
You don't!
13
13 is the unlucky
You don't. 13 is already prime.
1 x 13 and 13 x 1
Subtract 1999 from it.
Most children under 13 have an attempt to make one faking there age, My opinion is you to wait 'til you are 13 and check with your parents that you can make a Facebook.
338
No.
13
5 will make 12 and 13 a Pythagorean triad.