Running Time is WordPress plugin that can output details about the age of your blog using the date from your first post.
Running Time can output the date of the first post, the date of the last post, the date range of your posts and the age
of the blog measured in either days, weeks, months or years
Running Time 1.2 has been tested in WordPress 2.5, but still works with older versions of WordPress with the old category structure. It should also work in WordPress 2.0 with no problems, though untested.
Free Download: Download this wp-plugin