JSFiddle - React, Tailwind, and code Playground

HTML

<select name="start_year" id="start_year">
  <option value="2014">2014</option>
  <option value="2015">2015</option>
  <option value="2016">2016</option>
  <option value="2017">2017</option>
  <option value="2018">2018</option>
</select>

<select name="last_year" id="last_year">
  <option value="2014">2014</option>
  <option value="2015">2015</option>
  <option value="2016">2016</option>
  <option value="2017">2017</option>
  <option value="2018">2018</option>
</select>

JavaScript

$('document').ready(function() {
  $('#start_year').on('change', function() {
    var endage = $('#last_year option');
    var startageValue = this.value;
    var last=$('#last_year').val();
    
    
    endage.prop("disabled", false);
    
    if(startageValue === 0){
      return;
    }
    
    if(this.value < last)
    {
    alert('if');
    endage.each(function() {
    	if (this.value != 0 && this.value < startageValue) {
        $(this).prop("disabled", true);
      }
       });
    }

    else
    {
     endage.each(function() {

    alert('else');
    $('#last_year').val(startageValue);
      if (this.value != 0 && this.value < startageValue) {
        $(this).prop("disabled", true);
      }
          });

    }
    
    
    

    
  });




});