Although it’s difficult to ascertain, most SEO experts believe domain registration length is an SEO signal (as long as it points to a Live website) because Google filed a patent that stated;
“Certain signals may be used to distinguish between illegitimate and legitimate domains. … Valuable (legitimate) domains are often paid for several years in advance, while doorway (illegitimate) domains rarely are used for more than a year. Therefore, the date when a domain expires in the future can be used as a factor in predicting the legitimacy of a domain and, thus, the documents associated therewith.”
Google filed its patent for “DOCUMENT SCORING BASED ON DOCUMENT CONTENT UPDATE” at the same time they applied for the exclusive use of certain patent-able methods and processes back in 2011. See more about this cluster of patents here. See the actual patent here: https://patents.google.com/patent/US8549014B2/en
While this is often seen as a small factor, it is most notable when domains are in top-ranking positions start to lose ground as they approach an expiration date. The difference in rankings for a domain with 1-10 years until expiration vs. that of one with 90-30 days is quite dramatic.
Considering the low cost of domain registration, and the fact that Google has a patent stating they know how to and intend to use this information to determine rankings should make multi-year domain registration a no-brainer for most domain owners with an online business they expect to be in
While putting off your domain name's expiration date might help your search engine rankings, keep in mind that this may be only a small boost (or a "tie-breaker" among two websites) when it comes to the actual search engine rankings.
This is what makes it more important, the higher you rank for competitive keywords.