Yes, active what does it means?
My point of view of "active" means that user continues to interact with the community, posting content, and that his last post must not be older than a month.
if that is what you mean by active, then Theymos would be the oldest account that is active in the forum because while Sirius and BitcoinFX's "last active" date is shown as 2023 they haven't posted anything for a while now.