PHP код:
$v_link="SELECT *
FROM registration WHERE date_registered < NOW() - INTERVAL 14 DAY AND user_id='" . $HTTP_GET_VARS['user_id'] . "";
if (mysql_fetch_row(mysql_query($v_link))) {
echo "14 days is not passed";
} else {
echo "14 days is passed";
}
конечно можно и через массив