Internet meme that came about after some kid said it on a comment when Youtube.com was raided with porn. Usually said after something that adults talk about/kids wouldn't get. Not to be said in real life, like most other memes.
Anon A: I was wondering, do you guys prefer anal sex or vaginal sex?
Anon B: I'm 12 years old and what is this?
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Anon A: Do you think its worth it to have sex without a condom?
Anon B: I'm 12, what is this??
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Anon A: My girlfriend just blew me, shit was SO cash.
Sometimes used ironically on image boards like4chan when someone posts off topic or offensive material on a board where such content is inappropriate. This is usually posted in combination with sage to avoid bumping the thread.
anonA: Furry time!!!1 (explicit image of fluffy creatures)
anonB (sage): Please go away.
anonC (sage): I'm 12 and what is this?
A comment often left on older youtube music videos. A way for kids to congratulate themselves for listening to a song that is usually older than they are. They believe that this fact makes them better than everyone else, and smarter than anyone who listens to today's pop music.
Kid: OMG I'm only 12 and I'm listening to this song. I was born in the wrong generation!!!