Write log message when validation fails

When someone attempts to register and they enter a birthdate that fails validation, a log entry should be made recording the validation failure. It would be useful if the log included the birthdate that was entered that caused the validation failure.

Such a log entry would be a useful indicator of someone who has potentially lied to register.

Alternatively, a configuration option to send an e-mail message to the administrator would also suffice.

Basically, as an admin I want to know when an underaged person tries to access the site.