I need to calculate ages depended on birthday from a table of customers.

This is my code:

// customer age
function calculate_customer_age($startDate,$endDate){
    $endDate=date(m-d-y);
    $startDate= $customer['birthday'];
    $fromDate= new DateTime($startDate);
    $toDate= new DateTime($endDate);
    echo $fromDate->diff($toDate)->days;
}

In the last row, I need to echo age calculated depended on retrieve from a table of a customer from MySQL.

You can use below code in your function, which will calculate age upto today. You can modify $today to use the end date and format you want.

$dateOfBirth = $customer['birthday'];
$today = date("Y-m-d");
$diff = date_diff(date_create($dateOfBirth), date_create($today));
echo 'Age is '.$diff->format('%y');

You had several errors in your calculate_customer_age function, instead you can use the below code to get the difference in days between two dates:

function calculate_customer_age($startDate, $endDate)
{
    $startDate = DateTime::createFromFormat("m/d/Y", $startDate);
    $endDate = DateTime::createFromFormat("m/d/Y", $endDate);
    return $startDate->diff($endDate)->days;
}

echo calculate_customer_age("11/30/2008", "08/23/2018"); // 3553

Documentation:

• http://php.net/manual/en/class.datetime.php

There are many errors in your code. There is no need to pass end date in your function. You can use the following code to get the age.

function calculate_customer_age($startDate){
    $fromDate = new DateTime($startDate);
    $toDate       = new DateTime('today');
    return $fromDate->diff($toDate)->days;
       // or return $fromDate->diff($toDate)->y;
}

echo calculate_customer_age($customer['birthday']);

PHP >= 5.3.0

object oriented

$from = new DateTime('1970-02-01');
$to   = new DateTime('today');
echo $from->date_diff($to)->y;

procedural

echo date_diff(date_create('1970-02-01'), date_create('today'))->y;

MySQL >= 5.0.0

SELECT TIMESTAMPDIFF(YEAR, '1970-02-01', CURDATE()) AS age

If you want to calculate customer's age in days, you should do so:

function calculate_customer_age($startDate){
        $fromDate= new DateTime($startDate);
        $toDate= new DateTime();
        $difference = $fromDate->diff($toDate)->days;
        return $difference->format('%a');
}

php code

$startDate = '05-01-1988'; // sample start date or dob
$end_Date = '23-08-2018'; // smmple end date

echo calculate_customer_age( $startDate , $end_Date ); 

php function that returns age -

function calculate_customer_age( $startDate , $endDate ) //function returns age   
{   
    $diff = date_diff( date_create( $startDate  ), date_create( $endDate ) );
    return $diff->format('%y Years, %m Months, %d Days');
}

Sample Output :

30 Years, 7 Months, 18 Days