I don't have the ability to sort members by join date in my admin console. It wouldn't be that reliable anyway. Here's a little background for anyone interested:
Before 2004 I used a
different forum system that did not require registration. At the same time I was running Photopost that DID require registration. When I upgraded to the current forum software and CMS a database programmer helped me migrate the registered Photopost users into the new forum system before it was made public. When I did make the new forum public hundreds of more people who had been using the old system registered immediately. If you browse the old forum you'll see many of the same names/aliases that you see on the new forum.
If I could sort the members by join date the people at the top of the list would all be people who registered on Photopost in past years followed by hundreds of people who registered the day it was made public. That's why the list wouldn't really show what you're looking for.
You do have the ability to view the top posters. Pretty much everyone on that list was one of our original members.