Restrict users from editing post based on the age of the post

I took the example code from the WordPress user_has_cap filter codex page and modified it. Add this code to your theme functions.php:

function restrict_editing_old_posts( $allcaps, $cap, $args ) {

// Bail out if we're not asking to edit or delete a post ...
if( ( 'edit_post' != $args[0] && 'delete_post' != $args[0] )
  // ... or user is admin 
  || ! empty( $allcaps['manage_options'] )
  // ... or user already cannot edit the post
  || empty( $allcaps['edit_posts'] ) )
    return $allcaps;

// Load the post data:
$post = get_post( $args[2] );

// Bail out if the post isn't published:
if( 'publish' != $post->post_status )
    return $allcaps;

$post_date = strtotime( $post->post_date );
//if post is older than 30 days ...
if( $post_date < strtotime( '-30 days' )
  // ... or if older than 4 days and user is not Editor
  || ( empty($allcaps['moderate_comments']) && $post_date < strtotime('-4 days') ) ) {
    $allcaps[$cap[0]] = FALSE;
}
return $allcaps;
}
add_filter( 'user_has_cap', 'restrict_editing_old_posts', 10, 3 );