How to calculate age?

How could I calculate an person’s age if I have their year of birth?

Thanks heaps
Tim

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EDIT:

Im trying this function:

function age_in_years() {
	global $postmeta;
	$year_of_birth = get_field( "date_of_birth",$modelID);
	$date1 = strval( $year_of_birth );
	$date2 = strval( date( 'yy') );
	$age = $date2 = $date1;
	return $age;
}

But is not working at all… what I am doing wrong?
Using this code:
<?php echo age_in_years();?>

Is getting this:
05/07/1992

Database screenshot: https://i.imgur.com/mjLrEQx.png

https://www.ads-software.com/plugins/advanced-custom-fields/~

Waiting for your help, thanks ??