如何使用DatePicker设置年龄？

<input type="text" id="datepicker" />

$(document).ready(function() {
  $("#datepicker").datepicker({
    maxDate: new Date(),
    dateFormat: "yy-mm-dd"
  });
});

$(document).ready(function() {
  $("#datepicker").datepicker({
    maxDate: new Date(),
    dateFormat: "yy-mm-dd",
    onSelect: function(date) {
      var birthDate = new Date(date);
      var currentDate = new Date();
      var age = currentDate.getFullYear() - birthDate.getFullYear();
      // 判断是否已过生日
      if (currentDate.getMonth() < birthDate.getMonth() || (currentDate.getMonth() == birthDate.getMonth() && currentDate.getDate() < birthDate.getDate())) {
        age--;
      }
      $("#age").text("年龄：" + age);
    }
  });
});