$collection = Mage::getResourceModel('customer/customer_collection');
$collection->addAttributeToFilter('customer_products_changedate', 'OLDER THAN 14 DAYS');

$date = date('Y-m-d', strtotime('-14 day'));

$collection->addFieldToFilter(
    'customer_products_changedate',
    array(
        'lt'=>$date
    )
);