I disagree. My niche is very weak compared to other competitive niches, and I still cant rank above the 20 1998's websites above me. For ppc its no big deal, but for whitehat seo, if the gap is big, the factor is big as well.
There is one competing website, that is simply amazing in terms of content, domain age 1999. It ranks for everything in my niche. All the other sites have pretty much the same shitload of directory backlinks. I have three times more backlinks than the others, and the average PR of the sites linking to me is 5. And I still cant break through the old domains. I rank no1 for longtail, and relevant keywords.
So yes, domain age is a big factor from my experience.