- time: documentation ( source)
- mktime: documentation ( source)
- date: documentation ( source)
- strtotime: documentation ( source)
<?php
$birth = strtotime('10 march 2014');
$thisbd = mktime(0, 0, 0, date('n', $birth), date('j', $birth));
$lastbd = ($thisbd > time()) ? date('Y') - 1 : date('Y');
$age = $lastbd - date('Y', $birth);
echo $age;