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 changes 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?