See https://twitter.com/bearloga/status/1292899185604333568.

On profiles, "User Since" computes a relative time but it only goes up to weeks, so long-lived accounts have this kind of state information with some ridiculous number of weeks:

User Since Feb 7 2011, 5:28 PM (495 w, 6 d)

The rationale is that, given only a duration, you can accurately compute minutes, hours, days, and weeks by dividing, but can not accurately compute months or years (since a 30-day-old account may be "30 days" old if it was registered on January 1, or "1 month, 2 days" old if it was registered on February 1). However, reusing a duration function was only a clever shortcut until about April 2011 and is now just bizarre.