Wrong. Having the rank shows that you are active on the site - not how long you have been here.
It's really more of how active you've been since you joined. People with 7000 posts might not be active but they were. Reputation will better reflect you activeness because it goes down if you aren't active.
That's something that I don't like - if you go on a vacation then come back you've dropped down in reputation.
I don't like it much either. Maybe it will work like if you have been really active, and than completely inactive for a week, it won't matter. Or maybe it won't affect it as much as we think.