Here’s something I’ve wanted to know how to do since forever.

Use this trick to find files that have been modified since some arbitrary date:

$ touch -d "13 may 2001 17:54:19" date_marker
$ find . -newer date_marker

To find files created before that date, use the cnewer and negation conditions:

$ find . ! -cnewer date_marker

And to delete them, use the built-in “delete” action, eg:

$ find . ! -cnewer date_marker -delete

Discovered in the Irish Linux Users Group‘s exceptional online tutorial.