There is a myth that registering or renewing domain names for many years would actually help its ranking, and it looked like a good one to accept, but unfortunately we have a problem, it isn’t. Length of a domain registration won’t have a good impact on its ranking.
Google employee John Mueller suggested in a Google Webmaster Help forum thread that Google doesn’t look at the length of a domain registration, and also Google’s most familiar face Matt Cutts says the same. It’s not a factor to consider or worry about.
Here’s an interesting question “How much weight does the number of years a domain is registered for have on your ranking?”, and you can check out Matt Cutts’s reply for that in this video.
In a nutshell, what Matt said to that question is,
“To the best of my knowledge, no search engine has ever confirmed that they use length-of-registration as a factor in scoring. If a company is asserting that as a fact, that would be troubling.”
and also this,
“My short answer is not to worry very much about that [the number of years a domain is registered], not very much at all.”