The age of the domain name is the time the domain has existed since a record was first created on ICANN. An older domain is generally supposed to show more trust and commitment to a web site. More spammy sites usually will register a domain name for a year or so and then let it expire if the site fails or gets banned.
A great tool to check how old a domain name is can be found at Whois.sc.
Comments (1)
This is a great tip (i know from experience), and not very well known in most SEO circles.