... no one takes you seriously when your'e 12 and on the internet.
This sentence is wrong on two levels. First of all, it assumes that anyone on the Internet takes anyone seriously on the Internet. This is, sadly, true, but it really shouldn't be, at least for the vast majority of cases.
Second, unless you tell people, no one knows your age on the Internet. Even if you say how old you are, it's very difficult to prove it beyond all doubt. People might call you an X-year-old as an insult, but they can't prove it.
For example,
my profile says I'm twenty, but it's not technically impossible for me to be twelve, nineteen, twenty-two, thirty, or ninety-three. Admittedly, it's extremely implausible that I'm currently twelve, because that would mean I joined the forums when I was seven.