You can start submitting instantly, even with only a handful of articles. The more you have, the easier it is to start getting recognition from others however.
I've been actively involved in a number of NEW sites here in the past couple of months, and as soon as there's 5 articles I start the submission process and then go about the SEO of the website and getting more inbound links. Page Rank is used only by people these days, search engines don't pay any attention to it. Page Rank no longer means anything to Google. Page Rank Sculpting no longer works either - google removed all that fun stuff too
I can easily get a site with PR0 to rank number 1 and 2 in SERPs. Not only that, but you can easily rank a site with nothing more than RSS feeds from other sites and get those sites to outrank competition and use them as feeder sites.
Age no longer has ANYTHING to do with getting ranked in search engines. People that tell you that it takes a few weeks for your site to show up also are incorrect. Usually I can get a page on an existing site to show up within 20-60 minutes. A NEW sites I can get ranked and included in Google in less than 48 hours.
As for directory inclusion - it's nice, but not mandatory. Most paid services where you can be included in 1,000 directories for $49 or something are usually doing some automated system and that raises a red flag with directory sites and often can find the listing not listed. More hassle than it's worth.