Put this script in the HTML Area on the Registration Information page in your Teamraiser.

This removes future years from the select, and simulates the default validation on the birthdate fields on date change or submit.

<script>
	jQuery(document).ready(function ($) {

		if ( $("#cons_birth_date_YEAR").length ) {

			var thisYear = new Date().getFullYear();
			$("#cons_birth_date_YEAR option").each(function() {
				if ( $(this).val() > thisYear ) {
					$(this).remove();
				}
			});

			$("#cons_birth_date_YEAR, #cons_birth_date_MONTH, #cons_birth_date_DAY").change( function() { validateBirthday() });
			$("#F2fRegContact").submit( function(event) { if (validateBirthday()==false) event.preventDefault(); });

		}

		function validateBirthday() {
			if( $("#cons_birth_date_YEAR").val() && $("#cons_birth_date_MONTH").val() && $("#cons_birth_date_DAY").val() ) {
				var thisDate = new Date().getTime();
				var birthDate = new Date( $("#cons_birth_date_YEAR").val(), $("#cons_birth_date_MONTH").val(), $("#cons_birth_date_DAY").val() ).getTime();
				if ( birthDate >= thisDate ) {
					if ( $("#cons_info_dob.form-error").length == 0 ) {
						$("#cons_info_dob")
							.addClass("form-error")
							.prepend("<div class=\"ErrorMessage\">Must be in the past.</div>");
					}
					return false;
				} else {
					$("#cons_info_dob").removeClass("form-error");
					$("#cons_info_dob .ErrorMessage").remove();
					return true;
				}
			}
		}

	});
</script>