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.]
[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.]