Old blog postings now invisible to Google searches

Why can't I get any results searching for topics from older blog posts? AOL "powered by Google" can't find my old AOL Journal at all (0 results), and even older Blogger posts don't turn up any more. Do they "age off"? Even tagging doesn't change the results. I used to be able to look up when I wrote X (or someone else did) and link to it, but no more.