Also if you don't need the echo's to see what things are set to (which I'm thinking you don't since you didn't change the text, you could use Ternary to get it out of POST data. As such:
$partner = array();
$partner['bodytype'] = isset($_POST['partnerbodytype']) ? trim($_POST['partnerbodytype']) : NULL;
$partner['age'] = isset($_POST['partnerage']) ? $_POST['partnerage'] : NULL;
// .. etc etc
$missingfields = FALSE;
foreach($partner as $field) {
if( isnull($field) )
$missingfields = TRUE;
}
if( $missingfields ) {
/// display form again
} else {
/// process form
}