Well, as GHDPro has already said, AnimeSuki started on 26th December 2002. The forums have been around before that but not as an anime related site (that's why you can see members back from 2001), so the (real) forums are about a year old now.
There hasn't really been a need to do things like remove inactive users, while they do take up some storage space, it doesn't look like the we are running out of steam. It might happen in the future but who knows. I've been using the site since I discovered BT on 26th Jan 2003 (joined the forums on 29th Jan), a lot of new members have joined since then
BTW, is there a reason for your question?