how do I confirm old users retroactively with Devise?

I started using Devise without :confirmable. Now I've added it, and my users are being told to confirm their account, even though many have registered over a year ago.

I need to programmatically confirm all old users in the db. How can I do this?

You have to just set confirmed_at to some past date it will work fine. you can update confirmation_sent_at if you are going to use it for some other purpose like statistics.