OK, I've got an answer, from my developer:
We don't currently have any mechanism to allow this but what the user is trying to do is the right way to achieve it.
The code he has doesn't work because that's not how we store our field values but one way to do that right now is if the user figures out the field ID inside "Manage Form Fields" by looking at the id argument in the query string when trying to edit a field and uses that ID with some of the functions we have in the plugin, like wpbdp_get_listing_field_value() or wpbdp_get_listing_field_html_value().
Both receive as first argument the listing (post) ID and the field ID as second argument.
For instance, if the "age" field has ID 4, he could use something like this:
<?php $args=array('post_type' => 'wpbdp_listing', 'posts_per_page' => 10);
$loop = new WP_Query( $args );
while ($loop->have_posts()) : $loop->the_post();
<?php echo wpbdp_get_listing_field_html_value($post, 4); ?>
The difference between wpbdp_get_listing_field_value() and wpbdp_get_listing_field_html_value() is that the former retrieves the field value in raw format and the latter returns the value after some HTML transformations (for instance, turns URL field values into links and separates categories or tags linking each one to its own page).
Hope this helps.