Adsense age problem

Hi!

I just got 18 so now I'm allowed to legally use adsense on my websites. But when I try to sign up I get the next day a mail back with:

Issues: - Minimum age requirement

How do they check that? Or does someone has experience with this? I expect that emailing them won't work really fast. So I hope there is something else I can do.

Thanks in advance!