filtering existing search results - php

Question

I would like to create a search system that is able to filter general search results in more narrow way according to users specification.
For example, a user first performs general search of places and then the search system lists all users from that place and in the next step user wants to filter this user list according to the age.
The code below does general search for users from the specific place, and it also filters search results according to the age only if the keyword is specified in the search box and age group is selected before submitting.
What I want to achieve is that, users are able to filter results instantly after the general search is submitted. For example the general search results are John, Mary, Robert, and in the next step user selects age group 18-25 and the system instantly filters name John.
Any idea how to do this is very welcome!
This is php code:
<?php
include_once("php_includes/db_travel_vowel.php");
$search_output = "";
$search_output1 ="";
$username ="";
$age_form ="";
if(isset($_POST['searchquery']) && $_POST['searchquery'] != ""){
$searchquery = preg_replace('#[^0-9a-z]#i', '', $_POST['searchquery']);
$sqlCommand = "(SELECT * FROM users WHERE country LIKE '%$searchquery%' OR town LIKE '%$searchquery%' OR city LIKE '%$searchquery%')";
$query = mysqli_query($cn, $sqlCommand) or die(mysqli_error($cn));
$count = mysqli_num_rows($query);
if($count >= 1){
$search_output .= "<hr />$count results for <strong>$searchquery</strong><hr />";
while($row = mysqli_fetch_array($query)){
$url = $row["url"];
$f_name = $row["f_name"];
$l_name = $row["l_name"];
$user = $f_name;
$user.= " ";
$user.= $l_name;
$username = $row["username"];
if($_POST['age'] == "1" || $_POST['age'] == "2" || $_POST['age'] == "3" || $_POST['age'] == "4" || $_POST['age'] == "5" ){
$age=$_POST['age'];
$sqlC = "(SELECT f_name, l_name, url FROM users WHERE username='$username' AND age_group='$age')";
$query1 = mysqli_query($cn, $sqlC) or die(mysqli_error($cn));
while($row1 = mysqli_fetch_array($query1)){
$url1 = $row["url"];
$f_name1 = $row["f_name"];
$l_name1 = $row["l_name"];
$user1 = $f_name;
$user1.= " ";
$user1.= $l_name;
$username1 = $row["username"];
$search_output .= ''. $user1 .'<br>';
}
} else {
$search_output .= ''. $user .'<br>';
}
} // close while
} else {
$search_output = "<hr />0 results for <strong>$searchquery</strong><hr />$sqlCommand";
}
}
?>
HTML code:
<form id="search_new" action="index_search1.php" method="post">
<input name="searchquery" type="text" size="70" maxlength="88" placeholder="Search for places and members..." />
<input type="submit" />
<div id="options">
<select name="age">
<option selected>Age group<option>
<option value="1">18-28<option>
<option value="2">29-39<option>
<option value="3">40-50<option>
<option value="4">51-61<option>
<option value="5">62-more<option>
</select>
</div>
</form>
<?php echo $search_output; ?>
Thank you very much!