Subject: Domain registration period affecting SE rank
There are theories that a domain registration period affects its search engine trust and rank.
It is said that the longer your domain name is registered, the more search engines trust your site as a more long term effort and less of a 'hit and run' can spam kind of site.
It makes sense for it to be one among hundreds of possible factors, if I was building an algo I would make domain longevity a factor too.
Also keep in mind that Google has full access to domain registration details as they are a registrar, so they see more data that the average visitor doing a domain whois query, querying & integrating that data should be child's play for Google.
I just renewed my main site for 9 years and the DomainsByProxy subscription too for the same period totaling $170
I will report here if I observe positive changes apart from my peace of mind till year 2017 :-)