Set custom field to Members Search form and get result by that

bb_members_search.php

<?php


function bb_bp_ps_before_search_form( $F ) {

	$new            = new stdClass();
	$new->display   = 'selectbox';
	$new->code      = 'age_from'; // to be removed
	$new->html_name = 'age_from';
	$new->value     = '';
	$new->unique_id = bp_ps_unique_id( 'age_from' );
	$new->id = 0;
	$new->label = 'Age From';
	$new->options = array( 1 => 1, 2 => 2, 3 => 3, 4 => 4, );

	$F->fields[] = $new;
}

add_action( 'bp_ps_before_search_form', 'bb_bp_ps_before_search_form' );

function bb_bp_ps_field_sql( $sql, $f ) {

  // Do custom query for age.

  return $sql;

}

add_filter( 'bp_ps_field_sql', 'bb_bp_ps_field_sql', 10, 2 );