JSFiddle - React, Tailwind, and code Playground

HTML

<select id="countries">
   <option value="Albania">Albania</option>
   <option value="Algeria">Algeria</option>
   <option value="Argentina">Argentina</option>
   <option value="3">Armenia</option>
   <option value="4">Australia</option>
   <option value="5">Austria</option>
</select>
<br />
<label for="day">
   <span class="label-text" style="display: none;">Day</span> 
   <select name="day" id="day" class="placeholder av-select placeholder-inactive" title="Day">
      <option value="">DD</option>
      <option value="1">1</option>
      <option value="2">2</option>
      <option value="3">3</option>
      <option value="4">4</option>
      <option value="5">5</option>
      <option value="6">6</option>
      <option value="7">7</option>
      <option value="8">8</option>
      <option value="9">9</option>
      <option value="10">10</option>
      <option value="11">11</option>
      <option value="12">12</option>
      <option value="13">13</option>
      <option value="14">14</option>
      <option value="15">15</option>
      <option value="16">16</option>
      <option value="17">17</option>
      <option value="18">18</option>
      <option value="19">19</option>
      <option value="20">20</option>
      <option value="21">21</option>
      <option value="22">22</option>
      <option value="23">23</option>
      <option value="24">24</option>
      <option value="25">25</option>
      <option value="26">26</option>
      <option value="27">27</option>
      <option value="28">28</option>
      <option value="29">29</option>
      <option value="30">30</option>
      <option value="31">31</option>
   </select>
</label>
<label for="month">
   <span class="label-text" style="display: none;">Month</span> 
   <select name="month" id="month" class="placeholder av-select placeholder-inactive" title="Month">
      <option value="">MM</option>
      <option value="1">1</option>
      <option value="2">2</option>
      <option value="3">3</option>
      <option...

JavaScript

var countries = {
    "Albania": 18,
    "Algeria": 18,
    "Argentina": 21,
    "Armeria": 18,
    "Australia": 18,
    "Austria": 18
};

var individualCountry;
var day;
var month;
var year;

$("#verify").submit(function() {
    
    day = $("#day").val();
    month = $("#month").val();
    year = $("#year").val();
    
    var fullDate = day + month + year;
    console.log(fullDate);
    
    
    individualCountry = $("#countries").val();
    var ageLimit = countries[individualCountry];
    if (personsAge >= ageLimit) {
        
    }
    
    
})

//console.log(individualCountry);