Well, I like SeoMoz's survey of SEOs and their take on the
weight of SEO elements.
I'm not sure age of domain really matters any more ... I have seen a new site (less than 6 months old) come up to the top 10-20 for a highly competitive term recently and it is still climbing. No sandbox. The 3,000 backlinks to its blog probably has something to do with that ...
That said, I am not at all sure that this breaking down into percentages is useful, as you have to focus on all three elements: links (on and off site), content and optimization.