function get_tags_by_criteria($gender=\"%\", $min_age_of_birth=\"%\", $max_age_of_birth=\"%\", $country=\"%\", $region=\"%\", $city=\"%\", $tag=\"\") {
The CakePHP framework often uses associative arrays to specify a set of options. It will even let you specify either individual parameters or an associative array. See the find methods on the model class as an example.
Here's my attempt at making your function more flexible:
'ca',
'tag' => 'sample')); ?>