PornMD

Here's the pyramid of domain SEO quality as I see it based on factors that don't change, those being age, keywords in domain, and touching a bit on extension (as opposed to PR/backlinks/competition, which changes all the time). This is based on my own experience and what discussions with others have seemed to indicate - if you're trying to rank for a particular keyword phrase:

1. Exact match old domain (i.e. the keyword phrase, the whole phrase, nothing but the phrase, and should stick with com/net/org unless it's an insanely competitive term like "free porn").
2. Exact match new domain (simply put, exact matching domain rules regardless of age, but older is better, again stick with com/net/org unless insanely competitive term).
3. Old domain containing keyword phrase (i.e. word(s) + keyword phrase you're trying to rank for - .com by far most preferable in this case but net/org still aren't bad).
4. Old domain not containing keywords (you should go with short brandable or a catchy brandable phrases if you do this, not niche keywords completely unrelated to your site, only stick with .com unless you manage to get an extremely good net or org).
5. New domain containing keyword phrase (again this being word(s) + keyword phrase you're trying to rank for).
6. New domain not containing keyword phrase.

So - aged domains take up #1, #3, and #4 with the only infiltrating new domains being EXACT match (which take up #1 and #2 and illustrates that exact match really is the best move you can make). Yet so many people go for #5 and #6...which hey, if it's a shitty term with low traffic and/or relatively worthless traffic, you might still rank pretty easily if you do the other stuff right. But going after real terms, you're better suited trying to get an exact match and/or aged domain.

As far as how much age matters, IMO there's maybe 4 tiers: 10+ years old, 3-10 years old, 6 months to 3 years old, and 6 months or newer. In a lot of cases, if you're in the teens in age, then you'll be older than most if not all of the page 1 results for the phrase you're targeting unless it's major or in a really competitive industry in which case you may still have some really old competitors.

I make a living selling domains, I target exact match and aged domains in mostly com and org, and exact match domains have been the easiest to sell, even in .org, and even if they're fairly new domains. Aged domains however have been gaining steam as people realize it only goes up over time. After all, consider this - searches/mo, competition, and even value of traffic for a term can change, but age is firm and rarity of domains regged a certain year only goes up over time, with more of them dropping and more domains being registered overall meaning the % of domains regged in an aged year vs. overall registrations is in constant decrease.

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