Google looks at the age of your domain name as a small factor in your site’s ranking, and as a factor in evaluating how trustworthy it is. The reason they look at it is that spammers tend to look at their sites as throwaways. So they are very likely to buy a domain site (www.black-hat1.com), start getting some revenue from it, and as it gains traffic, they are already get started on the next site (www.black-hat2.com).
When the day comes that their www.black-hat1.com site gets flushed, www.black-hat2.com is already gaining in traffic. This is an effective way for them to stabilize their revenue and traffic, and not get to concerned when one of their sites gets blacklisted. Some people launch a new site every single week.
However, these types of sites don’t tend to stay around for very long. So looking at domain longevity can be a valuable data point for Google to use.
So assuming that you are looking to build your domain as a long term asset that contains lots of value, you can use this situation to your advantage. Just simply operating your site for a long time is helpful. If you have been running the domain for 3 years, 5 years, or more, you already have a little advantage (this assumes that the “theme” of the domain has remained consistent through that timeframe).
The other thing you can do is to register your domain for more than 1 year at a time. Guys who are launching a new site every week are less likely to register their sites for 10 years at a time. It becomes a real expense for them. It’s a small point, but a small expense for you, and a simple one to address, so why not? We need all the advantages we can get.