JSFiddle - React, Tailwind, and code Playground

HTML

<script src="http://manykeycs.16mb.com/jquery.datetimepicker.js"></script>
<link rel="stylesheet" href="http://manykeycs.16mb.com/jquery.datetimepicker.css">
      <label for="datetimepicker">Введите дату рождения</label><br>
      <input id="datetimepicker" type="text" id="date" /><br>
      <input type="button" id="enter" value="Посчитать" /><br>
      <textarea rows="6" cols="20" disabled></textarea>          
      <span class='info'></span>

JavaScript

$('#datetimepicker').datetimepicker({
   timepicker:false,
   lang:'ru',
   format:'d.m.Y',
});
$('#enter').click(function() {
  var en = $("#datetimepicker").val();
  var date = new Date();
  var dd = date.getDate()
  var mm = date.getMonth() + 1;
  var yy = date.getFullYear();
  var full = dd + "." + mm + "." + yy;
  var test = Math.round((date - en) / 864E5)
  $('.info').html("Результат\n. Сегодня " + full + " Дата рождения " + en + " Дней до ДР. " + test);
});