How to count dates (calculate age) in PHP (dates are stored in Unix Time)?

Question

PHP

You need to calculate the age based on the specified date of birth. Date of birth information is contained in Unix Time.
I'm not strong in PHP, I just started editing my existing code to get what I need.
Let me give you an example just to understand:

$tpl->set( '{birthday}', langdate( "D M Y", $row['birthday'] ) );

Displays the date of birth in the {birthday} tag accessible to the CMS , i.e. takes the Unix Time value from the string birthday and converts it to human readable D ate M onth Y ear. To display age, I want to create an {age}
tag accessible to CMS and display age through it. I guess in PHP it should look something like this:

$tpl->set( '{age}', текущая дата - $row['birthday'] ) );

But how to do it - no idea ...

Answer 1

/** @var \DateTime $dateBirth */
$diff = (new \DateTime())->diff($dateBirth);
$formatted = sprintf("%d лет", $diff->y);

Answer 2

function calculate_age($birthday) {
$birthday_timestamp = strtotime($birthday);
$age = date('Y') - date('Y', $birthday_timestamp);
if (date('md', $birthday_timestamp) > date('md')) {
$age--;
}
return $age;
}
echo calculate_age('1990-01-01');