I have heard that age of the domain is pretty relevant when it comes to search engine optimization. Apparently search engines (Google especially) boosts authority for old and established domains. Is this true and why?

Not just the age of the domain but also the expiration of the domain name will play a factor.

Google likes to see that someone has been around for a long time - that generally means authority on a subject. Also, if you have registered your domain name for many years out that will also give you a bonus as it shows that you're around to stay and not just testing the waters.

It probably plays a small role as part of Google's algorithm to determine the most relevant sites to show on the first page.

If a site is around for x number of years, then it's likely not to be some fly-by-night operation/spam page.

Just did a search on Google for web hosting providers and number 5 on page one shows their domain was created in April 2008 and expires in 2010. Have never done any real research to see what effect age has, but some swear it does and others don't. I have to believe it does play some role in their algorithms. Of the top seven, six had a longevity of at least four years.

Age of the domain does play a role, but I don't think it plays a huge role. There are so many different factors that play into search engine optimization.

SEO is too complicated

What i feel is Search engines would not give the advantage to Older domains, but to the domains that are most visited, which drives more traffic, older domains are indexed more times and hence can be useful for them

I have a partner in SEO biz, who says aged domains are very popular right now. I would have thought age is important but so too would be the age of the links a domain has had, over time. Google would probably be smart enough to be tracking such data, but nobody can say for sure (except google!).

I think that instead of domain age domain's content & backlinks are more important.

I've heard that it does play a role as well and honestly, it makes sense that it would take it into consideration but I think it's only a small factor. Still, when it comes to SEO, every little positive boost helps.

no that may have negative result it may be banned by gogle for example

And yet everything is so logical which proves how Google is smart in oppose to those times when it was still undeveloped enough. Today only the most educated experts in this field can achieve success.

I also have tried to search (but not very consistently) for some bigger industries and their web site expiration dates. This theory just proves to be accurate over and over.

+1 for them seeing that you are in it for the long run. So not just an aged domain, but registered ahead a ways as well.

we have two domains very old

www.internetbrothers.co.kr registered in 2001
and www.jafarnet.com registered in 1999

Well I hope the age of domain will effect ranking.