some one say so if do link build, age and authority should be consider? more: how to see if a site is authority.
Here you go: http://www.google.com/search?hl=en&q=digg Digg.com is an authority site! Google showing some extra URL's from Digg.
Domain age has always been important for Serps. Google also gives weight to how long the domain is registered. If you have a domain registered for 5 years and an equal site registered only for a year, Google gives more weight to the 5 year registration. Basically if you are looking for link building for the SERP and not for just PR, you want to find the best site you can that is related to your niche. It is easy to search Google and see who is on top for your niche and that is who you want to try to build a link to.