从出生日期开始计算山羊的年龄，并在表格上的字段中回声

I have a form with a dynamic select option. I want to calculate the age of a goat in months from its date of birth after selecting it from the db and echo the selected goat age on the following form field that follows the Dynamic selection option. Here is the selection script:

<?php 
$conn = mysqli_connect("localhost", "root", "xxx", "xxxx");
if(mysqli_connect_errno($conn)) {
echo "Unable to connect to database server";
}

$sql = "SELECT * FROM goats WHERE sex='Male'";
$query = mysqli_query($conn, $sql);

echo '<select name="hegoat">';
echo '<option value="">Choose He Goat</option>';
while($hegoats = mysqli_fetch_assoc($query)){
echo "<option>{$hegoats['goatid']}</option>";
}
echo '</select>';
?>

Data Base table is goats with 'dob' as the column for Date of Birth while the form field for age is:<input type="text" name="age" id="age"/>

And my PHP code is

<?php
if(isset($_POST['sub'])) 
{ 
    date_default_timezone_set ("Asia/Calcutta");
    $dateofreg1=date("d M Y");
    $dbd=$_POST['dob'];
    $startTimeStamp = strtotime($dbd);
    $endTimeStamp = strtotime($dateofreg1);
    $timeDiff = abs($endTimeStamp - $startTimeStamp);
    $numberDays = $timeDiff/86400;
    $numberDays = intval($numberDays);
    $days="Total day :".$numberDays;
    $birthDate =$dbd; 
    $birthDate = explode("/", $birthDate);
    $age = (date("md", date("U", mktime(0, 0, 0, $birthDate[0], $birthDate[1], $birthDate[2]))) > date("md") ? ((date("Y") - $birthDate[2]) - 1) : (date("Y") - $birthDate[2]));
    $dobs="Age is:" . $age; 
}
?>

As per your last comment, I am giving this answer.

 <?php if(isset($_POST['sub'])) 
    {
     date_default_timezone_set ("Asia/Calcutta");
    $dateofreg1=date("d M Y");
    $dbd=$_POST['dob'];
    $startTimeStamp = strtotime($dbd);
    $endTimeStamp = strtotime($dateofreg1);

    $year1 = date('Y', $startTimeStamp);   //select year1
    $year2 = date('Y', $endTimeStamp);    //select year 2
    $month1 = date('m', $startTimeStamp);   //month1
    $month2 = date('m', $endTimeStamp);      //month2
    $diff = (($year2 - $year1) * 12) + ($month2 - $month1);  //year*12 and month difference
     $dobs="Age is:" . $diff. "  months";
     ?>

Simple one line code for calculating days .

$Days = round(abs(strtotime($dob)-strtotime($currentDate))/86400);