Thanks apljdi! That worked, but I still had to put it in an array and get the last one, or it would return “Resource ID: #59.”
Here’s the final bit of code in case anyone ever needs to do this:
$info=mysql_query("SELECT post_content FROM wp_posts WHERE post_author = $userID ORDER BY post_date DESC LIMIT 1");
$array_content = mysql_fetch_array( $info );
$last_content = end($array_content);
echo $last_content;