One of them even signed up as far back as 6-26-1998.
There are also those who probably sign up a "new" account but leave it dormant anytime an account is banned.
Sign on date is no sign of a FReeper in good standing and the mods appear to be able to see just how long an account has been unused and what those last threads were.
I've seen at least one example of a profile too that had a false date (like 1776) as the signup date so it is possible that field could be hacked at one time.