$('#dateBirth').keyup(function(event){

	  var val = $(this).val().toString();
	  var patt = /[^0-9]/g;
	  var pure = val.replace(patt,"");
	  $(this).val(pure);
	  var val = $(this).val().toString();

	  var maxLength = Number($(this).attr('maxlength'));

	  if((event.which > 47 && event.which < 58) || (event.which > 95 && event.which < 105))  {
        if(val.length >= maxLength){
   	      if($(this)[0].id == $('#dateBirth')[0].id){
   	    	  $('#monthBirth').focus();
   	      }
   	      else if($(this)[0].id == $('#monthBirth')[0].id){
   	    	  $('#yearBirth').focus();
   	      }
        }
	  }

	  if(val.length > maxLength){
	      val = val.substring(0, maxLength);
	      $(this).val(val);
	  }

 }).blur(function(){

	  if ($(this).val() != "") {
		if ($(this).val() < 1) {
			$(this).val("1");
		} else {
			if (($(this)[0].id == $('#dateBirth')[0].id) && $(this).val() > 31){
				$(this).val("31");
			}
			else if (($(this)[0].id == $('#monthBirth')[0].id) && $(this).val() > 12){
				$(this).val("12");
			}
			else if (($(this)[0].id == $('#yearBirth')[0].id) && $(this).val() > 9999){
				$(this).val("9999");
			}
		}
		var val = $(this).val().toString();
		var length = val.length;
		var maxLength = Number($(this).attr('maxlength'));
		if (length < maxLength) {
			var i;
			for (i = 0; i < (maxLength - length); i++) {
				var val = $(this).val().toString();
				$(this).val('0' + val);
			}
		}
	}

  });

<div class="labelFieldWrapper dateBirth">
<input type="text" size="20" maxlength="2" id="dateBirth" name="birthDay" value="" class="inputElem js_movePlaceholder" />
</div>