For what it is worth, I have been managing one of my customers e-commerce sites since 1999. before Panda, 80% of it ranked in the top 5 search results with the remaining pages in the top 10. Since, Panda, it has fallen to page 2, 3 or further.
Shortly after Panda, a parallel site to the one above was launched, same design and content. It's pages rank as the old (existing) site did, for the most part. Despite some SEO changes to the original site, it has improved slightly, but still has not recovered fully. This has also happened to several customers of mine who have e-commerce sites, so I know it's not just me or my imagination.
My conclusion: Google was looking for fresh content and that a site's age, no matter how relevant the content, had little bearing on SERPs. One exception: large companies, e.g. that one site named after ancient warrior women, or a certain big box store.
I must emphasize, this is only in reference to an e-commerce site as several other non e-commerce sites I manage have not been affected at all.