Check WP_Query Order by Parameters
$args = array(
'post_type' => 'my_custom_post_type',
'meta_key' => 'age',
'orderby' => 'meta_value_num',
'order' => 'ASC',
'meta_query' => array(
array(
'key' => 'age',
'value' => array(3, 4),
'compare' => 'IN',
)
)
);
$query = new WP_Query($args);