##The information in this post is historically accurate but is no longer reflective of how close votes age away.
For the current logic (as of March 2, 2015), see: Age close votes after 14 days, regardless of views, allowing recasting
Start to age away at one per day immediately after there are 100 views*
This. There's no "view history" that'd tell us when a post crosses 100 views, so when the aging task fires it just looks at every post that has at least 100 views where all outstanding close votes are older than 4 days, and every post where all outstanding close votes are older than 14 days regardless of the view count.
Then it deletes the oldest close vote. A day later, it runs again and does the same thing, until either another close vote shows up, or all the close votes are deleted.
This works the same for reopen votes and "recommend close" flags.
The addition of the Close and Reopen /review queues adds another wrinkle to this though: if you get enough "Leave Open" or "Leave Closed" votes to complete the review, that also starts the aging process immediately - so four days after the last close or reopen vote was cast, they'll start getting deleted at the rate of one per day until they're all gone or a new one is added.