The google PageRank is a strange thing.
I have an old domain, a domain from my clan. The Clan was terminated in 2006 and I just have that domain that I do not lose the E-Mail addys. Now, I checked the PageRank and the result was 2. It’s really crazy, because the domain is not active sind 2006… But, the domain age is about 6 Years!
Following:
Don’t change your domain too often, the domain age is important for the PageRank!