How the new domain, old domain, expired domain effect SERP ?

[annua1]

I always heard the benefits of old domain on SERP in this forum and other forums like DP etc. Someone even claims not only domain age but also length of registration effect SERP. I'm totally confused about that, are they really stronger than other factors, say backlinks?

If so, I have some questions:
1) How does google determine domain's age, by whois or index date?
2) If a domain change ownership(whois), does google regard it a new domain?
3) If a domain expired several days(whois cleaned), then someone pick it up, does google regard it a new domain?
4) new domain with 10 years registration vs. 5 years old domain renewed every year, which one be favored by google?

[Xaver]

1) How does google determine domain's age, by whois or index date?

I suppose GG looks on the whois information for the domain age.

2) If a domain change ownership(whois), does google regard it a new domain?

No, a change of ownership is not a reset of the age in whois, so GG would not see it as new domain.

3) If a domain expired several days(whois cleaned), then someone pick it up, does google regard it a new domain?

Yes, expired domain are virtually new domains as there is no continuity from the previous registration.

4) new domain with 10 years registration vs. 5 years old domain renewed every year, which one be favored by google?

Domains registered for longer may be perceived as more serious projects. It is not very important factor in GG SERPs, but worth the money of extra years registration if you plan to make a long-term project.