Data validation on Birthdate and username?

[aquapyrofan]

Lately I've had some issues on my site with people either having malformed (as in, way too many slashes), improbable/impossible birth years (such as 1900 or 1003), and usernames with special characters (which probably won't validate against PMs and such properly). Is there any way to make sure the information they give is at least in the right format and/or the birth year is plausible before they sign up?