Editing older posts

My posts only have an "edit" button next to them if they're new. Could this be changed to enable editing of older posts? I think this would be useful (I also noticed in the "how to hide your email address from spammers" thread some people found they were unable to edit their unhidden email address out of older posts because of this).

There is a 24-hour limit on editing new posts. To avoid vandalism, older posts can be edited only if you contact the moderators.

Couldn't that be changed to just add a compulsory "this post was last edited by _____ [for _____ reason]" to edited posts?