filter search result to hide old posts

old-post-search-filter.php

function rkv_search_filter( $where = '' ) {
	// don't touch anything outside of a search query
	if(is_admin() || !is_search() )
		return $where;

	// Hide posts older than 2 years old
	if ( is_search() ){
		$where .= "AND post_type = 'post' AND post_date >= '" . date('Y-m-d', strtotime('-730 days')) . "'";
		return $where;
	}
}
add_filter('posts_where', 'rkv_search_filter');

would this be a good place to use a transient? ( just learning more about transients this week, trying to figure out when/where to use them )

Not really, because the search term would be different every time. You'd want to use a transient on a repeated query.

Thanks, that makes sense.

Take a look at the code in this plugin: https://github.com/norcross/gist-sidebar-widget I use transients there to store the API call so I don't hit the limits.