[losvedir]

Well there was that kid who lost access to his gmail account once he put his real birthday into G+.

[Drbble]

Because he was underage and it was illegal for Google to serve him email?

[pyre]

I don't think that it's technically illegal to serve email to someone under 13 years of age. That's just the conservative take on the law that most sites have taken.

[You may be able to allow < 13 year olds with parent's permission, but most sites probably feel that it's too much effort/risk to do that.]