I've heard that you get penalized in rankings for having a domain that is getting ready to expire within a year. How long should I register the domain to get maximum SEO benefits? 5 years? 10 years? or does anything over 1 year do?
I am not aware of any hard-and-fast, published guidelines. But it is commonly speculated that the search engines give some credit to those websites where the domains are paid up for more than one year. For what it's worth, I'm paid up until 2013, so I've put my money on the likelihood that domains paid up for multiple years do get some love from the SEs.
I read somewhere that domain registration for longer time meas stability. So google give some +ve points for it. Thought not sure... but it is logically correct.
It doesn't matter. You can have a newer domain rank just as well as an older one if you buld your site and promote it properly. The only reason why older domains are considered "trusted" is because they've had sufficient time to get quality relevant links pointing back to them.