I should clarify that this blog I posted:
Does Domain Age Affect Ranking
Refers to extending or purchasing additional years for your domain name has little if any impact in terms of ranking better. Which means that if I have a domain name that I just registered and I later decide to purchase 2 or more years additional registration it won't really help my Google rankings.
The same scenario can be said if I have a domain name that I have had for 10 years. If my domain name is 10 years old and I purchase a 1 year renewal it won't help me any more than if I purchase 2 or 5 additional years.
But...What many experts do agree on is how old or long you have had your domain can help you rank better. This seems to be most noticeable when comparing a brand new registered domain to one that has been around for several years.
Many believe that newly registered domains get sandboxed by Google. No matter what they do, or how much they optimize and tweak their site they remain in the sandbox until the site reaches some form of maturity. During this sandbox phase new sites will find it almost impossible to rank well or to get on page 1 in a Google search.
There is no specific time frame before a new site reaches maturity and is allowed out of the sandbox, but most experts believe it to be 6 months to 1 year time frame.
All you can do is be patient. Keep posting good useful quality content. You might try ranking for less popular keywords, or dabble into Yahoo and Bing's search optimization. Others recommended trying to purchase a domain name that is 1-2 years old or more, but this isn't always an option or solution.
If you don't seem to rank well in Google no matter how hard you try or what you do, it could very well be that your site is just too new yet and hasn't met Google's criteria for maturity.
Don't give up. Keep plugging away, and adding great new content. As time goes by Google will reward your site.