Age shortcode for WordPress

shortcode.php

function cheffism_age_function($atts) {
	extract(shortcode_atts(array(
		'date' => '12/31/1900', // DOB
		'format' => 'dd/MM/YYYY' // Format, does not currently do anything
	), $atts));

	//explode the date to get month, day and year
	$date = explode("/", $date);

	//get age from date or birthdate
	$age = (date("md", date("U", mktime(0, 0, 0, $date[1], $date[0], $date[2]))) > date("md") ? ((date("Y") - $date[2]) - 1) : (date("Y") - $date[2]));

	return $age;
}

add_shortcode('age', array( $this, 'cheffism_age_function') );