If I'm reading the responses correctly, it seems people here feel that links from different kinds of sites are aged differently.
For example, links from sites that are more of a social media, UGC or "periodical" type of site might start our strong and then begin to fade -- as in freshness matters a whole lot. But links from a site that is more conventional or static/stable can start modestly and then build over the next few months. That lines up with my gut feeling about it.
But then there's the question of links that age for years. My sense is that if the linking page goes stale, then the links get devalued. I even think there may be periodic sweeps through the entire webgraph to downgrade links from very old and stale pages.
its a bit dumb really, i think, if they downgrade links based on their age.
I agree, londrum - and that's why I don't think it's just age of the link that matters, but whether the linking page is still "alive" on the web - still getting soime clicks when it does get impressions, still attracting the occasional backlink, etc.