Hi,
For the fields "Category", "Brand", "Age group", "Gender", "Size" and "Color", you might need to have different values for different products. In that case, create a custom field of the table "product" via the menu Display->Custom field for each one of these options and instead of entering the value in the option of the plugin, you would enter here the corresponding custom product field's column name. Then, in each product you would enter the value you want in the custom fields.
The plugin would then automatically pick the corresponding values in the products for these fields.
The availability of the products is already inferred automatically from the quantity field of the products. If all items are identified as "in stock" by the plugin, it means that all the products have a quantity different from 0. It's working fine on our end.
For the condition, the plugin doesn't handle yet different values for different products. You would have to change the line:
$xml.="\t".'<g:condition><![CDATA[ '.$plugin->params['condition'].' ]]></g:condition>'."\n";
by:
$xml.=$this->_additionalParameter($product,$plugin,'condition','condition');
in the file plugins/hikashop/google_product/google_product.php and then the plugin would handle that.